Analytical differentiation in for loops

Hello,

When I run the below with Master(i,1) replaced by Master(1,1) code runs with no errors.

Master = [1000, 2000, 5000, 10000, 20000, 50000, 100000, 200000, 500000, 1e6, 2e6, 5e6, 10e6; 100, 200, 500, 1000, 2000, 5000, 10000, 20000, 50000, 1e5, 2e5, 5e5, 10e5];
syms x1
GRs = 200;
Rss = Master(1,1)+GRs*Master(1,1)*x1; 
dRs = diff(Rss, x1);
dRs2 = diff(Rss^2, x1); 
dRs_val = vpa(subs(dRs,x1,0));
dRs2_val = vpa(subs(dRs2,x1,0)); 

As soon as I put into for loop like below:

Master = [1000, 2000, 5000, 10000, 20000, 50000, 100000, 200000, 500000, 1e6, 2e6, 5e6, 10e6; 100, 200, 500, 1000, 2000, 5000, 10000, 20000, 50000, 1e5, 2e5, 5e5, 10e5];
for i = 1:length(Master)
    syms x1
    GRs = 200;
    Rss = Master(i,1)+GRs*Master(i,1)*x1; 
    dRs = diff(Rss, x1);
    dRs2 = diff(Rss^2, x1); 
    dRs_val = vpa(subs(dRs,x1,0));
    dRs2_val = vpa(subs(dRs2,x1,0)); 
end

I get the following error: NaN/Inf breakpoint hit for symvar.m on line 33.

33 n = inf;

Even after clearing workspace usinf the diff function on simple expressions copied from ttps://www.mathworks.com/help/symbolic/differentiation.html return same error. Restart fixes this issue.

Where am I going wrong?

[Torsten]

Please include the complete executable code so that we are able to reproduce the error.

[Peter]

Updated. Thanks for suggestion.

[Walter Roberson]

Which MATLAB version are you using? Current releases do not have any inf in symvar.

[Peter]

R2020a is that helps

[Walter Roberson]

I do not happen to have R2020a installed, but I checked R2019b and R2020b and symvar.m in them does not have any assignment of inf

Is it possible that you have Maple installed?

Answer 1

[Taylor]

You have an indexing issue. Master is a 2x13 array. By indexing to Master(i,1) you are exceeding the index bounds once you go past i=2. Change Master(i,1) to Master(1,i) and the code will run.

Master = [1000, 2000, 5000, 10000, 20000, 50000, 100000, 200000, 500000, 1e6, 2e6, 5e6, 10e6; 100, 200, 500, 1000, 2000, 5000, 10000, 20000, 50000, 1e5, 2e5, 5e5, 10e5];
for i = 1:length(Master)
    syms x1
    GRs = 200;
    Rss = Master(1,i)+GRs*Master(1,i)*x1; 
    dRs = diff(Rss, x1);
    dRs2 = diff(Rss^2, x1); 
    dRs_val = vpa(subs(dRs,x1,0));
    dRs2_val = vpa(subs(dRs2,x1,0))
end