Joe Riel

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14 years, 143 days

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These are replies submitted by Joe Riel

Show an example of what you have done.

Could you upload the msim here?  Use the green arrow.

I cannot tell what you really want, but suspect that assign(Equate(C,A)); would achieve it. The effect of the assign is to create a procedure named c with a remember table.

@aaeerr First, I copied that code from the displayed code shown in the code region in the Equation Extraction app, then added the statement at the end.  The code goes into a worksheet that is linked to the MapleSim model. You could also run it standalone, in a separate Maple worksheet, by changing the first statement to something like

A := MapleSim:-LinkModel('filename' = "HW4.msim"):

then continuing with the other commands. Here's a brief explanation of what each line does

Connect to the the MapleSim model. A is assigned a Maple module with exports that allow interacting with the linked model.

A := MapleSim:-LinkModel('filename' = "MW4.msim"):

Select the subsystem of interest. This isn't necessary because you are interested in the entire model.

A:-SetSubsystemName(""):

Define shorter names for the parameters and variables of interest. You can use A:-GetParameters('allparams') to list all the parameters, and A:-GetVariables() for the variables.

A:-SetSubstitutions([`Main.SpringDamper.c` = c__SpriD, `Main.SpringDamper.d` = d__SpriD, `Main.SpringDamper.phi_rel0` = PhiR0__SpriD, `Main.Revolute.M`(t) = M__Revolute(t), `Main.Revolute.theta`(t) = theta__Revolute(t)], 'nocheck'):

Get the equations. See the help page for LinkModel,GetEquations for the options.

eqs := A:-GetEquations('output' = 'all', 'inputs' = {}, 'filter' = [], 'simplify' = true, 'params' = {`Main.SpringDamper.c`, `Main.SpringDamper.d`}):

Get the differential-algebraic equations. Note that the lhs should really be named daes; the displayed code has a typo which prevents the next line (in the app, not here) from working.

dae := eqs[1];

Call isolate to isolate the variable M__Revolute(t) in the second equation in daes (this assumes the ordering is consistent, which may not be case) to the lhs, then call subs to eliminate it from the first equation.

subs(isolate(dae[2],M__Revolute(t)), dae[1]);

@Basak My mistake.  I had put your code in a procedure to permit easier debugging but didn't declare all variables as globals.  Doing so masks your problem. What is actually happening is that tj is assigned NULL. Put a print statement after the call to tj := solve(eqtj,tj) and you'll see the problem.  Maybe that should be solve(eqtj, p)?

@acer A chance for the rarely used mul:

mul(GE[i,i],i=1..2)

@acer Nice extension.

@acer Both solutions offered use the determinant.  Suppose the set only consisted of three vectors (of dimension 4).

@Carl Love The bigger problem with that many positional parameters is that it is hard to visually check whether the call is correct. A way around that is to use keyword parameters, the call is then sort of self-documenting.  The same issue arises when using a vector or array to group values; for that reason I generally prefer using a record.  Debugging and maintaining is generally easier when you can associate a meaning with a value.

@assma Thanks for the explanation.  I don't have 2017.0 immediately available to check it on; it looks fine in 2018.2. What OS are you using?

Explain what you think is wrong.  The plot in the worksheet is correct for the given input.

@Kitonum I'm thinking maybe the posted worksheet is not what he has. Or possibly he doesn't realize that, after calling the assign procedure, the values of a and b are assigned so that the evaluation of v(x) does not have a literal a and b (they are globals, not arguments of v), but rather their numeric values. If the latter is the issue, then a and b can be unassigned, say with

a := a': b := 'b':
v(x);
     -1/2*x^2-1/6*x^3+a*x+b

I don't understand what you think is wrong.

@acer Good point, I hadn't noticed that. It would be safe to use RK__1, which will look the same in 2D output.

Consider uploading your mw file here.  Use the green up arrow.

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