trunk/doc/howto-model3.lyx

#LyX 1.4.1 created this file. For more info see http://www.lyx.org/
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\language english
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\quotes_language english
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\end_header

\begin_body

\begin_layout Chapter
Creating a plot
\begin_inset LatexCommand \index{plot}

\end_inset

 (using a library model
\begin_inset LatexCommand \index{library model}

\end_inset


\begin_inset LatexCommand \index{model, library}

\end_inset

) 
\begin_inset LatexCommand \label{cha:model3}

\end_inset


\end_layout

\begin_layout Standard
In this chapter we are going to produce a plot by using a model that someone
 else has created.
 We gain two lessons: (1) you will understand first hand the difficulties
 one encounters when trying to use a model someone else has created and
 (2) you will learn how to produce a plot in ASCEND.
 The approach we take is not the one you should take if your goal is simply
 to produce this plot.
 Our goal is pedagogical
\begin_inset LatexCommand \index{pedagogical}

\end_inset

, not efficiency.
 In the last chapter we created an array of vessel models to produce the
 data that we now about to plot.
 We approached this problem this way so you could see how one creates arrays
 in ASCEND.
 Having this model, we have the data.
 The easiest thing we can do now it use it to produce a plot.
\end_layout

\begin_layout Standard
We also have in ASCEND the ability to do case studies over a model instance,
 varying one or more of the fixed variables for it over a range of values
 and capturing the values of other variables that result.
 This powerful case study tool is the proper way to produce this plot as
 ASCEND only has to compile one instance and solve it repeatedly rather
 than produce an array of models.
 We finish this chapter showing you how to use this case study tool.
\end_layout

\begin_layout Section
Creating a plot
\end_layout

\begin_layout Standard
We want a plot of 
\family typewriter
metal_mass
\family default
 values vs.
 
\family typewriter
H_to_D_ratio
\family default
.
 If we look around at the available tools, we find there is a 
\series bold
Plot
\series default
 tool
\begin_inset LatexCommand \index{tool, Plot}

\end_inset


\begin_inset LatexCommand \index{Plot tool}

\end_inset

 under the 
\series bold
Display
\series default
 button in the Browser window.
 While not obvious, it turns out we can plot the arrays we produce when
 we include instances of type 
\family typewriter
plt_plot_integer
\family default

\begin_inset LatexCommand \index{plt\_plot\_integer}

\end_inset

 and 
\family typewriter
plt_plot_symbol
\family default

\begin_inset LatexCommand \index{plt\_plot\_symbol}

\end_inset

 in our model.
 We find these types in the file 
\family typewriter
plot.a4l
\family default
 located in the ASCEND4 models directory which is distributed with ASCEND.
 Figure 
\begin_inset LatexCommand \ref{fig:model3.plot.a4l}

\end_inset


\noun off
 is a print out of that file (but with line numbers added so we can reference
 them here).
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout LyX-Code
REQUIRE "system.a4l";
\end_layout

\begin_layout LyX-Code
PROVIDE "plot.a4l";
\end_layout

\begin_layout LyX-Code
(* some lines removed here...
 *)
\end_layout

\begin_layout LyX-Code

\end_layout

\begin_layout LyX-Code
(*=============================================================================*
\end_layout

\begin_layout LyX-Code
 P L O T .
 A 4 L
\end_layout

\begin_layout LyX-Code
 ---------------
\end_layout

\begin_layout LyX-Code
AUTHOR:Ben Allan
\end_layout

\begin_layout LyX-Code
provoked by plot.lib by Peter Piela and Kirk A.
 Abbott
\end_layout

\begin_layout LyX-Code
DATES:03/97 - Original code.
\end_layout

\begin_layout LyX-Code
CONTENTS:
\end_layout

\begin_layout LyX-Code
A parameterized plot library mostly compatible
\end_layout

\begin_layout LyX-Code
with plot.lib, but with variable graph titles.
\end_layout

\begin_layout LyX-Code
*)
\end_layout

\begin_layout LyX-Code
MODEL pltmodel() REFINES cmumodel();
\end_layout

\begin_layout LyX-Code
END pltmodel;
\end_layout

\begin_layout LyX-Code
MODEL plt_point(
\end_layout

\begin_layout LyX-Code
x WILL_BE real;
\end_layout

\begin_layout LyX-Code
y WILL_BE real;
\end_layout

\begin_layout LyX-Code
) REFINES pltmodel();
\end_layout

\begin_layout LyX-Code
END plt_point;
\end_layout

\begin_layout LyX-Code
(***************************************************************)
\end_layout

\begin_layout LyX-Code
MODEL plt_curve(
\end_layout

\begin_layout LyX-Code
npnts IS_A set OF integer_constant;
\end_layout

\begin_layout LyX-Code
y_data[npnts] WILL_BE real;
\end_layout

\begin_layout LyX-Code
x_data[npnts] WILL_BE real;
\end_layout

\begin_layout LyX-Code
) REFINES pltmodel();
\end_layout

\begin_layout LyX-Code
(* points of matching subscript will be plotted in order of
\end_layout

\begin_layout LyX-Code
 * increasing subscript value.
\end_layout

\begin_layout LyX-Code
 *)
\end_layout

\begin_layout LyX-Code
legendIS_A symbol; (* mutable now! *)
\end_layout

\begin_layout LyX-Code
FOR i IN [npnts] CREATE
\end_layout

\begin_layout LyX-Code
pnt[i]IS_A plt_point(x_data[i],y_data[i]);
\end_layout

\begin_layout LyX-Code
END FOR;
\end_layout

\begin_layout LyX-Code
END plt_curve;
\end_layout

\begin_layout LyX-Code
(***************************************************************)
\end_layout

\begin_layout LyX-Code
MODEL plt_plot_integer(
\end_layout

\begin_layout LyX-Code
curve_set IS_A set OF integer_constant;
\end_layout

\begin_layout LyX-Code
curve[curve_set] WILL_BE plt_curve;
\end_layout

\begin_layout LyX-Code
) REFINES pltmodel();
\end_layout

\begin_layout LyX-Code
title, XLabel, YLabel IS_A symbol; (* mutable now! *)
\end_layout

\begin_layout LyX-Code
Xlow IS_A real;
\end_layout

\begin_layout LyX-Code
Ylow IS_A real;
\end_layout

\begin_layout LyX-Code
Xhigh IS_A real;
\end_layout

\begin_layout LyX-Code
Yhigh IS_A real;
\end_layout

\begin_layout LyX-Code
Xlog IS_A boolean;
\end_layout

\begin_layout LyX-Code
Ylog IS_A boolean;
\end_layout

\begin_layout LyX-Code
END plt_plot_integer;
\end_layout

\begin_layout LyX-Code
(***************************************************************)
\end_layout

\begin_layout LyX-Code
MODEL plt_plot_symbol(
\end_layout

\begin_layout LyX-Code
curve_set IS_A set OF symbol_constant;
\end_layout

\begin_layout LyX-Code
curve[curve_set] WILL_BE plt_curve;
\end_layout

\begin_layout LyX-Code
) REFINES pltmodel();
\end_layout

\begin_layout LyX-Code
title, XLabel, YLabel IS_A symbol; (* mutable now! *)
\end_layout

\begin_layout LyX-Code
Xlow IS_A real;
\end_layout

\begin_layout LyX-Code
Ylow IS_A real;
\end_layout

\begin_layout LyX-Code
Xhigh IS_A real;
\end_layout

\begin_layout LyX-Code
Yhigh IS_A real;
\end_layout

\begin_layout LyX-Code
Xlog IS_A boolean;
\end_layout

\begin_layout LyX-Code
Ylog IS_A boolean;
\end_layout

\begin_layout LyX-Code
END plt_plot_symbol;
\end_layout

\begin_layout Caption
The file plot.a4l
\begin_inset LatexCommand \index{plot.a4l}

\end_inset


\begin_inset LatexCommand \label{fig:model3.plot.a4l}

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
As you can see, this file contains the two types we seek -- starting in
 lines 59 and 71, respectively.
 However, before we can use them, we do need to understand them.
 We are, so to speak, on the receiving end of the reusability issue.
 If you spend some time, you will find that you can decipher these model
 definitions.
 To make that less painful, we will help you do so here.
 If these models were better documented, they would be much less difficult
 to interpret.
 In time we will add Notes to them to remedy this deficiency.
\end_layout

\begin_layout Subsection
Model refinement
\begin_inset LatexCommand \index{refinement}

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Marginal
status collapsed

\begin_layout Standard
please, explain "refines"
\end_layout

\end_inset

The first model, pltmodel, is two lines long, having a MODEL statement indicatin
g it "refines" cmumodel and an END statement.
 We have not encountered the concept of refinement as yet.
 In ASCEND the to refine means the model pltmodel inherits all the statements
 of cmumodel, a model which has been defined at the end of the file 
\family typewriter
system.a4l
\family default
.
 We show the code for cmumodel in Figure 
\begin_inset LatexCommand \ref{fig:model3.cmumodel}

\end_inset


\noun off
, and we note that it too is an empty model.
 It is, as it says, a root for a collection of loosely related models.
 You will note (and forgive) a bit of dry humor by its author, Ben Allan.
 So far as we know, this model neither provokes nor hides any bugs.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout LyX-Code
MODEL cmumodel();
\end_layout

\begin_layout LyX-Code
(* This MODEL does nothing except provide a root
\end_layout

\begin_layout LyX-Code
 * for a collection of loosely related models.
\end_layout

\begin_layout LyX-Code
 * If it happens to reveal a few bugs in the software,
\end_layout

\begin_layout LyX-Code
 * and perhaps masks others, well, what me worry? 
\end_layout

\begin_layout LyX-Code
 * BAA, 8/97.
\end_layout

\begin_layout LyX-Code
 *)
\end_layout

\begin_layout LyX-Code
END cmumodel;
\end_layout

\begin_layout Caption
The code for cmumodel
\begin_inset LatexCommand \index{cmumodel}

\end_inset


\begin_inset LatexCommand \label{fig:model3.cmumodel}

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
We need to introduce the concept of type refinement to understand these
 models.
 We divert for a moment to do just that.
\end_layout

\begin_layout Standard
\begin_inset Marginal
status collapsed

\begin_layout Standard
parents
\begin_inset LatexCommand \index{parents}

\end_inset

 and children
\begin_inset LatexCommand \index{children}

\end_inset

 in a refinement hierarchy
\end_layout

\end_inset

Suppose model B refines model A.
 We call A the parent model and B the child.
 The child model B inherits
\begin_inset LatexCommand \index{}

\end_inset

 all the code defining the parent model A.
 In writing the code for model B, we do not write the code it inherits from
 A; we simply understand it is there already.
 The code we write for model B will be only those statements that we wish
 to add beyond the code defining its parent.
 ASCEND supports only single inheritance; thus a child may have only one
 parent.
 A parent, on the other hand, may have many children, each inheriting its
 code.
 
\end_layout

\begin_layout Standard
\begin_inset Marginal
status collapsed

\begin_layout Standard
order does not matter in nonprocedural code
\begin_inset LatexCommand \index{nonprocedural code}

\end_inset


\end_layout

\end_inset

We are dealing in ASCEND with models defined by their variables and equations.
 As we have noted above, the order for the statements defining each of these
 does not matter -- i.e., the variables and equations may be defined in any
 order.
 So adding new variables and equations through refinement may be done quite
 easily.
 
\end_layout

\begin_layout Standard
\begin_inset Marginal
status collapsed

\begin_layout Standard
but it does in the procedural code
\begin_inset LatexCommand \index{procedural code}

\end_inset

 for methods
\end_layout

\end_inset

In constrast, the methods are bits of procedural code -- i.e., they are run
 as a sequence of statements where order does matter.
 In ASCEND, a child model will inherit all the methods of the parent.
 If you wish to alter the code for a method, you must replace it entirely,
 giving it the same name as the method to be replaced.
 (However, if you look into the documentation on the language syntax for
 methods, you will find that the original method is still available for
 execution.
 You simply have to add a qualifier to its name to point to it.)
\end_layout

\begin_layout Standard
If we look into this file we see the refinement hierarchy
\begin_inset LatexCommand \index{refinement hierarchy}

\end_inset


\begin_inset LatexCommand \index{hierarchy, refinement}

\end_inset

 shown in Figure 
\begin_inset LatexCommand \ref{fig:model3.refineHierPlot.a4l}

\end_inset


\noun off
.
 
\noun default
'
\noun off
cmumodel
\noun default
'
\noun off
 is the parent model for all these models.
 pltmodel is its child.
 The remaining three models are children of pltmodel.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Standard

\noun off
\InsetSpace ~
\InsetSpace ~
\InsetSpace ~
\InsetSpace ~
\InsetSpace ~
\InsetSpace ~
\InsetSpace ~
\InsetSpace ~
\InsetSpace ~
\InsetSpace ~

\begin_inset Graphics
    filename howto-model3Fig3.eps

\end_inset


\end_layout

\begin_layout Caption
The refinement hierarchy in the file plot.a4l
\begin_inset LatexCommand \label{fig:model3.refineHierPlot.a4l}

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
reasons for refinement
\end_layout

\end_inset

There are three reasons to support model refinement, with the last being
 the most important one.
\end_layout

\begin_layout Itemize
We write more compact code
\begin_inset LatexCommand \index{compact code}

\end_inset

: The first reason is compactness of coding.
 One can inherit a lot of code from a parent.
 Only the new statements belonging to the child are then written to define
 it.
 This is not a very important reason for having refinement.
\end_layout

\begin_layout Itemize
Changes we make to the parent propagate
\begin_inset LatexCommand \index{propagate}

\end_inset

: A second reason is that one can edit changes into the parent and know
 that the children will inherit those changes without having to alter the
 code written for the child.
 (Of course, one can change the parent in such a way that the changes to
 the child are not what is wanted for the child, introducing what will likely
 become some interesting debugging problems.)
\end_layout

\begin_layout Itemize
\begin_inset Marginal
status collapsed

\begin_layout Standard
with the most important being we know what can substitute for what
\end_layout

\end_inset

We know what can substitute
\begin_inset LatexCommand \index{substitute}

\end_inset

 for what: The most important reason is that inheritance tells us what kinds
 of parts may be substituted for a particular part in a model.
 Because a child inherits all the code from its parent, we know the child
 has all the variables and equations defined for it that the parent does
 -- and typically more.
 We can use an instance of the child as a replacement for an instance of
 the parent.
 Thus if you were to write a model with the part A1 of type A in it, someone
 else can create an instance of your model and substitute a part B1 which
 is of type B.
 This substituted part will have all the needed variables in it that you
 assumed would be there.
\end_layout

\begin_layout Standard
This third reason says that when a object passed as a parameter 
\family typewriter
WILL_BE
\family default
 of type A, we know that a part of either type A or type B will work.
\end_layout

\begin_layout Subsection
Continuing with creating a plot
\end_layout

\begin_layout Standard
We are going to include in our model a part of type 
\family typewriter
plt_plot_integer
\family default
 or 
\family typewriter
plt_plot_symbol
\family default
 that ASCEND can plot.
 We need to look at the types of parameters required by whichever of these
 two we select to include here.
 Tracing back to its parents, we see them to be empty so all the code for
 these types is right here.
\end_layout

\begin_layout Standard
The first parameter we need is a 
\family typewriter
curve_set
\begin_inset LatexCommand \index{curve\_set}

\end_inset


\family default
 which is defined to be a set of 
\family typewriter
integer_constant
\family default
 or of 
\family typewriter
symbol_constant
\family default
.
 We have to guess at this time at the purpose for 
\family typewriter
curve_set
\family default
.
 It would really help to have notes defining the intention here and to have
 a piece of code that would demonstrate the use of these models.
 At present, we do not.
 We proceed, admitting we will appear to "know" more than we should about
 this model.
 It turns out that 
\family typewriter
curve_set
\family default
 allows us to identify each of the curves we are going to plot.
 These models assume we are plotting several variables (let's call them
 y[1], y[2], ...) against the same independent variable x.
 The values for curve_set are the '1', '2', etc.
 identifying these curves.
\end_layout

\begin_layout Standard
Here we wish to plot only one curve presenting 
\family typewriter
metal_mass
\family default
 vs.
 
\family typewriter
H_to_D_ratio
\family default
.
 We can elect to use 
\family typewriter
plt_plot_symbol
\family default

\begin_inset LatexCommand \index{plt\_plot\_symbol}

\end_inset

 and label this curve '5 mm'.
 The label '5 mm' is a symbol so we will create a set of type symbol with
 this single member.
\end_layout

\begin_layout Standard
The second object has to be a object of type 
\family typewriter
plt_curve
\family default
.
\end_layout

\begin_layout Standard
Looking at line 45, we see how to include an object of type 
\family typewriter
plt_curve
\family default
.
 It must be passed three objects: a set of integers (e.g., the set of integers
 from 1 to 20) and two lists of data giving the y-values vs.
 the x-values for the curve.
 In the model tabulated_vessel_values, we have just these two lists, and
 they are named 
\family typewriter
metal_mass
\family default
 and 
\family typewriter
H_to_D_ratio
\family default
.
\end_layout

\begin_layout Standard

\noun off
You need now to add to the model tabulated_vessel_values
\noun default
 in Figure 
\begin_inset LatexCommand \ref{fig:model3.vesselPlot}

\end_inset


\noun off
 
\noun default
(it is saved as vesselPlot.a4c
\begin_inset LatexCommand \index{vesselPlot.a4c}

\end_inset

).

\noun off
 It contains a part called 
\family typewriter
\noun default
massVSratio
\family default
\noun off
 of type 
\family typewriter
\noun default
plt_plot_symbol
\family default
\noun off

\begin_inset LatexCommand \index{plt\_plot\_symbol}

\end_inset

 that ASCEND can plot.
 This code is at the end of the declarative statements in tabulated_vessel_value
s.
 It also replaces the first method, 
\family typewriter
\noun default
default_self
\family default
\noun off
.
\noun default
]
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout LyX-Code
CurveSet "the index set for all the curves to be plotted"
\end_layout

\begin_layout LyX-Code
            IS_A set OF symbol_constant;
\end_layout

\begin_layout LyX-Code
    CurveSet :== ['5 mm'];
\end_layout

\begin_layout LyX-Code

\end_layout

\begin_layout LyX-Code
    Curves['5 mm'] 
\end_layout

\begin_layout LyX-Code
      "the one curve of 20 points for metal_mass 
\backslash

\end_layout

\begin_layout LyX-Code
       vs.
 H_to_D_ratio"
\end_layout

\begin_layout LyX-Code
            IS_A plt_curve(
\end_layout

\begin_layout LyX-Code
               [1..n_entries], 
\end_layout

\begin_layout LyX-Code
               metal_mass, 
\end_layout

\begin_layout LyX-Code
               H_to_D_ratio
\end_layout

\begin_layout LyX-Code
               ); 
\end_layout

\begin_layout LyX-Code
    massVSratio "the object ASCEND can plot"
\end_layout

\begin_layout LyX-Code
            IS_A plt_plot_symbol(
\end_layout

\begin_layout LyX-Code
               CurveSet, 
\end_layout

\begin_layout LyX-Code
               Curves
\end_layout

\begin_layout LyX-Code
               );
\end_layout

\begin_layout LyX-Code
    
\end_layout

\begin_layout LyX-Code
METHODS
\end_layout

\begin_layout LyX-Code
METHOD default_self;
\end_layout

\begin_layout LyX-Code
(* set the title for the plot and the labels
\end_layout

\begin_layout LyX-Code
   for the ordinate and abscissa *)
\end_layout

\begin_layout LyX-Code
    massVSratio.title :=
\end_layout

\begin_layout LyX-Code
     'Metal mass of the walls vs H to D ratio 
\backslash

\end_layout

\begin_layout LyX-Code
         for a thin-walled cylindrical vessel';
\end_layout

\begin_layout LyX-Code
    massVSratio.XLabel := 'H to D ratio';
\end_layout

\begin_layout LyX-Code
    massVSratio.YLabel := 'metal mass IN kg/m^3';
\end_layout

\begin_layout LyX-Code
END default_self;
\end_layout

\begin_layout Caption
The last bit of new code to include a plot in the model tabulated_vessel_values
 
\begin_inset LatexCommand \label{fig:model3.vesselPlot}

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
Also just after the first line in this file -- which reads
\end_layout

\begin_layout LyX-Code
REQUIRE "atoms.a4l";
\end_layout

\begin_layout Standard
place the instruction
\end_layout

\begin_layout LyX-Code
REQUIRE "plot.a4l";
\end_layout

\begin_layout Standard
When you solve this new instance and make massSVratio the current object,
 you will find the Plot tool under the Display button in the Browser window
 lights up and can be selected.
 If you do this, you will get a plot of metal_mass vs.
 H_to_D_ratio.
 A clear minimum is apparent on this plot at H_to_D_ratio equal to approximately
 one.
\end_layout

\begin_layout Standard
You should create a script to run this model just as you did for vesselTabulated.
a4c in the previous chapter.
 Save it as vesselPlot.a4s.
\end_layout

\begin_layout Section
Creating a case study from a single vessel
\end_layout

\begin_layout Standard
You may think creating an array of vessels and a complex plot object just
 to generate a graph is either an awful lot of work or a method which will
 not work for very large models.
 You think correctly on both points.
 The 
\family typewriter
plt_plot
\family default
 models are primarily useful for sampling values from an array of inter-related
 models that represent a spatially distributed system such as the pillars
 in a bridge or the trays in a distillation column.
 You can conduct a case study, solving a single model over a range of values
 for some specified variable, using the Script command 
\family typewriter
STUDY
\family default
.
 
\end_layout

\begin_layout Standard
We will step through creating a base case and a case study using the vessel
 model.
 Start by opening a new buffer in the Script window and turning on the record
 button of the Scripts edit menu.
 In the Library window run the Delete all types button to clear out any
 previous simulations.
 Load the vessel model from the file vesselMethods.a4c you created in Section
 3.2.
 
\end_layout

\begin_layout Subsection
The base case
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
compile a vessel
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Select and compile the vessel model.
 Give the simulation the name V.
 Select the simulation V in the bottom pane of the Library window and use
 the right mouse button (or Alt-x b) to send the simulation to the Browser.
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
solving the base case
\end_layout

\end_inset


\end_layout

\begin_layout Standard
In the Browser, place the mouse cursor over the upper left pane.
 Use the right mouse button to run methods reset and values, then send the
 model to the Solver by typing Alt-x s.
 Move the mouse to the Solver window and hit the F5 key to solve the model.
 
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
graphical case study optimization
\end_layout

\end_inset


\end_layout

\begin_layout Standard
We now know that it takes 535.7 kg of metal to make a 250 cubic foot vessel
 which is twice as high as it is broad.
 Suppose that now we want to know the largest volume that this amount of
 metal can contain assuming the same wall thickness is required.
 Perhaps a skinnier or fatter vessel can hold more, so we need to do a case
 study using the aspect ratio (H_to_D_ratio) as the independent variable.
 Use the Browser to change V.metal_mass.fixed to TRUE, since we are using
 a constant amount of metal.
 The solver will want you to free a variable now, so select V.vessel_vol
 to be freed, since volume is what we want to study.
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
script recorded so far
\end_layout

\end_inset


\end_layout

\begin_layout Standard
Turn off the recording button on the Script window.
 The recording should look something like
\end_layout

\begin_layout LyX-Code
DELETE TYPES;
\end_layout

\begin_layout LyX-Code
READ FILE {vesselMethods.a4c};
\end_layout

\begin_layout LyX-Code
COMPILE V OF vessel;
\end_layout

\begin_layout LyX-Code
BROWSE {V};
\end_layout

\begin_layout LyX-Code
RUN {V.reset};
\end_layout

\begin_layout LyX-Code
SOLVE {V} WITH QRSlv;
\end_layout

\begin_layout LyX-Code
ASSIGN {V.metal_mass.fixed} TRUE {};
\end_layout

\begin_layout LyX-Code
# you must type the next line in the script yourself.
\end_layout

\begin_layout LyX-Code
ASSIGN {V.vessel_vol.fixed} FALSE {};
\end_layout

\begin_layout Standard
The file ascend4/models/vesselStudy.a4s was recorded in a similar manner.
\end_layout

\begin_layout Subsection
Case study examples
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
configuring a case study
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The STUDY command takes a lot of arguments.
 Well explain them all momentarily, but should you forget them simply enter
 the command STUDY without arguments in the ASCEND Console window or xterm
 window to see an error message explaining the arguments and giving an example.
 Enter the following command in the Script window exactly as shown except
 for the file name following OUTFILE.
 Specify a file to be created in your ascdata directory.
\end_layout

\begin_layout LyX-Code
STUDY {vessel_vol} 
\backslash

\end_layout

\begin_layout LyX-Code
IN {V} 
\backslash

\end_layout

\begin_layout LyX-Code
VARYING {{H_to_D_ratio} {0.1} {0.5} {0.8} {1} {1.5} {2} 
\backslash

\end_layout

\begin_layout LyX-Code
{3} {4} {8}} 
\backslash

\end_layout

\begin_layout LyX-Code
USING {QRSlv} 
\backslash

\end_layout

\begin_layout LyX-Code
OUTFILE {/usr0/ballan/ascdata/vvstudy.dat} 
\backslash

\end_layout

\begin_layout LyX-Code
ERROR STOP;
\end_layout

\begin_layout Standard
This is the simplest form of case study; the backslashes at the end of each
 line mean that it is all one big statement.
 Select all these lines in the Script at once with the mouse and then hit
 F5 to execute the study.
 The solver will solve all the cases and produce the output file vvstudy.dat.
 The quickest way to see the result is to enter the following command in
 the Script, then select and execute it.
 (Remember to use the name of your file and not the name shown).
\end_layout

\begin_layout LyX-Code
ASCPLOT {/usr0/ballan/ascdata/vvstudy.dat};
\end_layout

\begin_layout LyX-Code
ASCPLOT CLOSE; #omit if you want to see data table
\end_layout

\begin_layout Standard
You should get a graph that looks something like Figure 4-5
\begin_inset LatexCommand \ref{fig:StudyVolumeVsHtoD}

\end_inset

.
 The largest volume is in the neighborhood of an H_to_D_ratio of 1.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Standard
\begin_inset Graphics
    filename howto-model3Fig5.eps
    scale 80
    BoundingBox 50bp 0bp 600bp 430bp

\end_inset


\end_layout

\begin_layout Caption
Study of Volume as Function of H/D
\begin_inset LatexCommand \label{fig:StudyVolumeVsHtoD}

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Subsubsection
Multi-variable studies
\end_layout

\begin_layout Standard
We now have an idea where the solution is most interesting, so we can do
 a detailed study where we also monitor other variables such as surface
 areas.
 Additional variables to watch can be added to the STUDY clause of the statement.
\end_layout

\begin_layout LyX-Code
STUDY {vessel_vol} {end_area} {side_area} 
\backslash

\end_layout

\begin_layout LyX-Code
IN {V} 
\backslash

\end_layout

\begin_layout LyX-Code
VARYING {{H_to_D_ratio} {0.5} {0.6} {0.7} {0.8) {0.9} 
\backslash

\end_layout

\begin_layout LyX-Code
{1} {1.1} {1.2} {1.3}} 
\backslash

\end_layout

\begin_layout LyX-Code
USING {QRSlv} 
\backslash

\end_layout

\begin_layout LyX-Code
OUTFILE {/usr0/ballan/ascdata/vvstudy.dat} 
\backslash

\end_layout

\begin_layout LyX-Code
ERROR STOP;
\end_layout

\begin_layout LyX-Code
ASCPLOT {/usr0/ballan/ascdata/vvstudy.dat};
\end_layout

\begin_layout LyX-Code
ASCPLOT CLOSE; #omit if you want to see data table
\end_layout

\begin_layout Subsubsection
Multi-parameter studies
\end_layout

\begin_layout Standard
We can also do a multi-parameter study, for example also varying the wall
 thickness allowed.
 In general, any number of the fixed variables can be varied in a single
 study, but be aware that ASCENDs relatively simple plotting capabilities
 do not yet include surface or contour maps so you will need another graphic
 tool to view really pretty pictures.
\end_layout

\begin_layout LyX-Code
STUDY {vessel_vol} 
\backslash

\end_layout

\begin_layout LyX-Code
IN {V} 
\backslash

\end_layout

\begin_layout LyX-Code
VARYING 
\backslash

\end_layout

\begin_layout LyX-Code
{{H_to_D_ratio} {0.8) {0.9} {1} {1.1} {1.2} {1.3}} 
\backslash

\end_layout

\begin_layout LyX-Code
{{wall_thickness} {4 {mm}} {5 {mm}} {6 {mm}} {7 {mm}}} 
\backslash

\end_layout

\begin_layout LyX-Code
USING {QRSlv} 
\backslash

\end_layout

\begin_layout LyX-Code
OUTFILE {/usr0/ballan/ascdata/vvstudy.dat} 
\backslash

\end_layout

\begin_layout LyX-Code
ERROR STOP;
\end_layout

\begin_layout LyX-Code
ASCPLOT {/usr0/ballan/ascdata/vvstudy.dat};
\end_layout

\begin_layout Standard
In this study the peak volume occurs at the same H_to_D_ratio for any wall
 thickness but the vessel volume increases for thinner walls.
 This may be hard to see with the default graph settings, but column 2 in
 rows 8-11 (H_to_D = 1.0) of the ASCPLOT data table have the largest volumes
 for any given thickness in column 1.
 Notice that the units must be specified for the wall_thickness values in
 the VARYING clause.
\end_layout

\begin_layout Subsubsection
Plotting output with other tools
\end_layout

\begin_layout Standard
To convert the study results from the ASCPLOT format to a file more suitable
 for importing into a spreadsheet, the following command does the trick.
 As usual, change the names to match your ascdata directory.
\end_layout

\begin_layout LyX-Code
asc_merge_data_files excel 
\backslash

\end_layout

\begin_layout LyX-Code
{/usr0/ballan/ascdata/vvs.txt} 
\backslash

\end_layout

\begin_layout LyX-Code
{/usr0/ballan/ascdata/vvstudy.dat}
\end_layout

\begin_layout Standard
If you prefer Matlab style text, substitute matlab for excel in the line
 above and change the output name from vvs.txt to vvs.m.
\end_layout

\begin_layout Subsection
STUDY behavior details
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
variable list
\end_layout

\end_inset


\end_layout

\begin_layout Standard
We now turn to the details of the STUDY statement.
 As we saw in Section 4.2.2.1, any number of variables to be monitored can
 follow the STUDY keyword.
 
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
IN clause
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The IN clause specifies which part of a simulation is to be sent to the
 Solver; a small part of a much larger model can be studied if you so desire.
 All the variable and parameter names that follow the STUDY keyword and
 that appear in the VARYING clause must be found in this part of the simulation.
 
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
parameter list
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The VARYING clauses is a list of lists.
 Each inner list gives the name of the parameter to vary followed by its
 list of values.
 Each possible combination of parameter values will be attempted in multi-parame
ter studies.
 If a case fails to solve, then the study will behave according to the option
 set in the ERROR clause.
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
solver name
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The solver named in the USING clause is invoked on each case.
 The solver may be any of the algebraic solvers or optimizers, but the integrato
rs (e.g.
 LSODE) are not allowed.
 
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
data file name
\end_layout

\end_inset


\end_layout

\begin_layout Standard
The case data are stored in the file name which appears in the OUTFILE clause.
 By default, this file is overwritten when a STUDY is started, so if you
 want multiple result files, use separate file names.
\end_layout

\begin_layout Standard
\begin_inset Marginal
status open

\begin_layout Standard
error handling
\end_layout

\end_inset


\end_layout

\begin_layout Standard
When the solver fails to converge or encounters an error, the STUDY can
 either ignore it (ERROR IGNORE) and go on to the next case, warn you (ERROR
 WARN) and go on to the next case, or stop (ERROR STOP).
 The ERROR option makes it possible start a case study and go to lunch.
 Cases which fail to solve will not appear in the output data file.
\end_layout

\begin_layout Standard
Note that if the model is numerically ill-behaved it is possible for a case
 to fail when there is in fact a solution for that combination of parameters.
 STUDY uses the solution of the last successfully solved case as the initial
 guess for the next case, but sometimes this is not the best strategy.
 STUDY also does not attempt to rescale the problem from case to case.
 When a case that you think should succeed fails, go back and investigate
 that region of the model again manually or with a more narrowly defined
 study.
\end_layout

\begin_layout Section
Discussion
\end_layout

\begin_layout Standard
We have just led you step by step through the process of creating, debugging
 and solving a small ASCEND model.
 We then showed you how to make this model more reusable, first by adding
 comments and methods.
 Methods capture the "how you got it well-posed" experience you had when
 first solving an instance of the vessel model.
 We then showed you how to parameterize this model and then use it to construct
 a table of 
\family typewriter
metal_mass
\family default
 values vs.
 
\family typewriter
H_to_D_ratio
\family default
 values.
 Finally we showed you how to add a plot of these results.
 You should next look at the chapter in the documentation where you create
 two more small ASCEND models.
 This chapter gives you much less detail on the buttons to push.
 Finally, if you are a chemical engineer, you should look at the chapter
 on the script and model for a simple flowsheet (
\family typewriter
simple_fs.a4s
\family default
 and 
\family typewriter
simple_fs.a4c
\family default
 respectively).
 
\end_layout

\begin_layout Standard
With this experience you should be ready to write your own simple ASCEND
 models to solve problems that you might now think of solving using a spreadshee
t.
 Remember that once you have the model debugged in ASCEND, you can solve
 inside out, backwards and upside down and NOT just the way you first posed
 it -- unlike your typical use of a spreadsheet model.
\end_layout

\end_body
\end_document