Simulink error: The NAME input must be a constant

Sorry for the trivial question. I was coding my intergeneration time action in entity generator block in Simulink. I was certaint this bit of code will work because I tested it in Matlab. But instead I got this error from the diagnostic viewer.

Error in 'task06/Entity Generator ' block. See Intergeneration time action line 5, column 6.

Caused by:

The NAME input must be a constant.

Component:Simulink | Category:Block error

This is my code:

u = repelem([0.1; 5; 10; 15; 20; 35],[204 145 18 2 1 1]);

pd = fitdist(u,"Exponential");

dt = random(pd)

I wonder what's wrong? I ran it on Matlab and it worked everytime. TIA.

[Walter Roberson]

Experiment with

u = repelem([0.1; 5; 10; 15; 20; 35],[204 145 18 2 1 1]);
pd = fitdist(u,'Exponential');
dt = random(pd)

[Stanley Martin Siagian]

@Walter Roberson

Thanks for the input, but correct me if I'm wrong, are you only correcting the quotation mark from a pair to one? I tried that but the same error still appears.

[Walter Roberson]

There are some cases (or have been historically) in which the code generation facilities support single-quoted character vectors but not double-quoted string objects.

[Walter Roberson]

I notice that if you

help random

then it talks strictly about "Name" as the first parameter. That leads me to suspect that at that point in the code, Simulink thinks you are invoking

toolbox/stats/stats/random.m

when instead you are invoking a method inside

toolbox/shared/statslib/+prob/TruncatableDistribution.m

As a debugging step, I suggest trying

u = repelem([0.1; 5; 10; 15; 20; 35],[204 145 18 2 1 1]);
pd = fitdist(u,'Exponential');
disp(which('random(pd)'))
dt = 0;   %so you can actually execute without it complaining about dt not being defined

[Stanley Martin Siagian]

@Walter Roberson

Sorry for the late response. I've done exactly as you written but apparently Simulink doesn't support the 'which' and the 'help' function.

Error in 'task06/Entity Generator ' block. See Intergeneration time action line 1, column 1.

Caused by:

• Function 'help' not supported for code generation.

Component:Simulink | Category:Block error

Error in 'task06/Entity Generator ' block. See Intergeneration time action line 5, column 6.

Caused by:

• Function 'which' not supported for code generation.

Component:Simulink | Category:Block error

Answer 1

[Tridib]

Hi @Stanley Martin Siagian,

I verified that Simulink is interpreting the call to “random” as referring to the function in “toolbox/stats/stats/random.m” which expects "Name" as the first input rather than the method from “toolbox/shared/statslib/+prob/TruncatableDistribution.m”.

1. As an alternative, the distribution can be precomputed and samples can be generated in advance:

% in MATLAB Workspace, before simulation 
u = repelem([0.1; 5; 10; 15; 20; 35],[204 145 18 2 1 1]); 
pd = fitdist(u, "Exponential"); 
precomputed_dt = random(pd, 1000,1);  % generate a big vector of samples 
assignin('base','precomputed_dt',precomputed_dt);  % put into base workspace 

2. Within the Intergeneration time action, those precomputed values can then be used as follows:

% persistent idx keeps the value of idx between calls, so it remembers  
% which part of precomputed_dt to use next during the simulation. 
persistent idx; 

if isempty(idx) 
    idx = 1;   
end 

dt = precomputed_dt(idx); 
idx = idx + 1; 

if idx > length(precomputed_dt) 
    idx = 1; % Loop 
end 

3. If your goal is just "random exponential delay", you can replace your code with:

dt = exprnd(mean(u)); 

For more help, refer to the following documentation:

persistent: https://www.mathworks.com/help/matlab/ref/persistent.html

assignin: https://www.mathworks.com/help/matlab/ref/assignin.html

exprnd: https://www.mathworks.com/help/stats/exprnd.html

Hope this helps!