SglPend: Broken Code Gen. by balacij · Pull Request #4396 · JacquesCarette/Drasil

balacij · 2025-10-07T21:00:47Z

This PR highlights some bizarre behaviour. This is not a PR that is intended to be merged anytime soon. It is a PR meant to highlight issues. Once SglPend's code generation works, then we can merge this PR (or a PR that replaces this one).

balacij · 2025-10-07T21:27:19Z

code/stable/sglpend/src/cpp/Control.cpp

+int main(int argc, const char *argv[]) {
+    string filename = argv[1];
+    double L_rod;
+    double m;
+    double α;
+    double θ_p;
+    double θ_i;
+    double p_x^i;
+    double p_y^i;
+    get_input(filename, L_rod, m, α, θ_p, θ_i);
+    derived_values(L_rod, θ_i, p_x^i, p_y^i);
+    input_constraints(L_rod, θ_i);
+    write_output(θ_p);


Invalid variable names. Conventional C++ does not use unicode characters. Additionally '^' is an operator not permitted in the name of variables.

get_inputs confused me for a second. We pass in variable names but they're automatically turned into references. I'm not sure if I'm a fan of not explicitly rendering something that indicates it is going to be passed as reference and could be mutated...

The only output is one of the inputs.

That sure is weird - probably ought to create 3 issues for each of those.

For 1, the C++ generator ought to error out. And the solution is to have the names use the features of Drasil that let you have different renderings in code vs spec. Other examples use that already.

balacij · 2025-10-07T21:27:56Z

code/stable/sglpend/src/java/SglPend/Control.java

+        double θ_i;
+        double p_x^i;
+        double p_y^i;
+        Object[] outputs = InputParameters.get_input(filename);


outputs = Input...

Ah, this is making sense now:

inputs :: [DefinedQuantityDict] inputs = map dqdWr [lenRod, QPP.mass, QP.angularAccel, pendDisplacementAngle, initialPendAngle] outputs :: [DefinedQuantityDict] outputs = [dqdWr pendDisplacementAngle]

Hey, Drasil does exactly what it was asked to do! Fancy that!

Probably pendDisplacementAngle should not be an input.

Removing pendDisplacementAngle from the inputs list:

sglpend: The following outputs cannot be computed: pendDisplacementAngle Unused definitions are: pendDisplacementAngle, frequency, angularFrequency, period Known values are: l_rod, mass, angularAcceleration, initialPendAngle, ixPos, iyPos CallStack (from HasCallStack): error, called at lib/Language/Drasil/CodeSpec.hs:258:20 in drasil-code-0.1.9.0-CVigL3PxUMa78erpyMb2gY:Language.Drasil.CodeSpec

See my comments on the issue about the right way to fix this.

initialPendAngle (which corresponds to $\theta_i$) is already in the inputs list.

Note: I didn't look into this further yet.

balacij · 2025-10-07T21:29:02Z

code/stable/sglpend/src/java/SglPend/Control.java

+        p_x^i = (double)(outputs[0]);
+        p_y^i = (double)(outputs[1]);
+        InputParameters.input_constraints(L_rod, θ_i);
+        OutputFormat.write_output(θ_p);


Only θ_p is used, and it doesn't even have any constraints. We don't need to generate any of the other code.

JacquesCarette · 2025-10-07T21:58:21Z

code/stable/sglpend/src/cpp/Control.cpp

+int main(int argc, const char *argv[]) {
+    string filename = argv[1];
+    double L_rod;
+    double m;
+    double α;
+    double θ_p;
+    double θ_i;
+    double p_x^i;
+    double p_y^i;
+    get_input(filename, L_rod, m, α, θ_p, θ_i);
+    derived_values(L_rod, θ_i, p_x^i, p_y^i);
+    input_constraints(L_rod, θ_i);
+    write_output(θ_p);


That sure is weird - probably ought to create 3 issues for each of those.

JacquesCarette · 2025-10-07T22:00:24Z

code/stable/sglpend/src/cpp/Control.cpp

+int main(int argc, const char *argv[]) {
+    string filename = argv[1];
+    double L_rod;
+    double m;
+    double α;
+    double θ_p;
+    double θ_i;
+    double p_x^i;
+    double p_y^i;
+    get_input(filename, L_rod, m, α, θ_p, θ_i);
+    derived_values(L_rod, θ_i, p_x^i, p_y^i);
+    input_constraints(L_rod, θ_i);
+    write_output(θ_p);


For 1, the C++ generator ought to error out. And the solution is to have the names use the features of Drasil that let you have different renderings in code vs spec. Other examples use that already.

JacquesCarette · 2025-10-07T22:01:36Z

code/stable/sglpend/src/csharp/Control.cs

+        InputParameters.get_input(filename, out L_rod, out m, out α, out θ_p, out θ_i);
+        InputParameters.derived_values(L_rod, θ_i, out p_x^i, out p_y^i);
+        InputParameters.input_constraints(L_rod, θ_i);
+        OutputFormat.write_output(θ_p);


At least the csharp is consistent with the C++!

JacquesCarette · 2025-10-07T22:03:13Z

code/stable/sglpend/src/java/SglPend/Control.java

+        double θ_i;
+        double p_x^i;
+        double p_y^i;
+        Object[] outputs = InputParameters.get_input(filename);


Hey, Drasil does exactly what it was asked to do! Fancy that!

Probably pendDisplacementAngle should not be an input.

smiths · 2025-10-10T14:06:01Z

Do single pendulum and double pendulum take advantage of sharing any code, the way that SWHS and noPCM share code?

balacij · 2025-10-10T20:03:39Z

There is a bit of sharing in the SglPend -> DblPend direction, and some common sharing from drasil-data, similar to the other examples.

drasil-example/sglpend/lib/Drasil/SglPend/Goals.hs
13: import Drasil.DblPend.Concepts (rod)

drasil-example/sglpend/lib/Drasil/SglPend/Assumptions.hs
5:import Drasil.DblPend.Assumptions (assumpBasic)

drasil-example/sglpend/lib/Drasil/SglPend/Unitals.hs
17:import Drasil.DblPend.Concepts (rod)
18:import Drasil.DblPend.Unitals (lRod)

drasil-example/sglpend/lib/Drasil/SglPend/Body.hs
22:import Drasil.DblPend.Body (justification, externalLinkRef, charsOfReader,
26:import Drasil.DblPend.Concepts (concepts, rod)
27:import Drasil.DblPend.Requirements (nonFuncReqs)
28:import Drasil.DblPend.Unitals (acronyms)
29:import Drasil.DblPend.References (citations)

drasil-example/sglpend/lib/Drasil/SglPend/Requirements.hs
9:import Drasil.DblPend.Requirements(verifyInptValsDesc)

drasil-example/sglpend/lib/Drasil/SglPend/GenDefs.hs
32:import Drasil.DblPend.Concepts (arcLen, horizontalPos,

drasil-example/sglpend/lib/Drasil/SglPend/DataDefs.hs
15:import Drasil.DblPend.Concepts (horizontalPos, verticalPos)

It looks like it's primarily sharing English definitions and a few quantities (the .Unitals imports). Do you want me to dissect this further?

smiths · 2025-10-21T21:19:53Z

@balacij, don't investigate further. You have enough on your plate right now. 😄 Thank you for starting the process of getting SglPend working properly. This might be a good task for a future summer research assistant. 😄

SglPend: Broken Code Gen.

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balacij commented Oct 7, 2025

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JacquesCarette reviewed Oct 7, 2025

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balacij self-assigned this Oct 7, 2025

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balacij commented Oct 7, 2025

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smiths commented Oct 10, 2025

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balacij commented Oct 10, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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balacij commented Oct 10, 2025 •

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