What is ind2sub

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Varun Nair
Varun Nair on 19 Jul 2021
Edited: Walter Roberson on 23 Jul 2021
This is the code where I had doubt on the syntax of ind2sub
A=0.01; %Wb is the unit of A
B=0.001; %H is the unit of Inductance
I =(0:1:2); %row!
theta=(0:1:45).'; %column!
T = - A .* I .* cosd(theta) + B .* I.^2 .* sind(2*theta);
surf(I, theta, T)
xlabel('I'); ylabel('theta'); zlabel('Torque')
[maxT, idx] = max(T(:));
[r,c] = ind2sub(size(T), idx);
best_theta = theta(r);
best_I = I(c);
fprintf('best torque is %g at theta = %g and I = %g\n', maxT, best_theta, best_I);

Accepted Answer

Star Strider
Star Strider on 20 Jul 2021
Edited: Walter Roberson on 23 Jul 2021
MATLAB uses linear indexing for arrays, however many arrays are also referred to by subscripts into the rows, columns, and additional dimensions. The ind2sub function converts the linear indices into subscripts.
In this example:
[maxT, idx] = max(T(:));
[r,c] = ind2sub(size(T), idx);
the ind2sub call takes linear index ‘idx’ and converts it to the appropriate subscripts into matrix ‘T’. (It appears to be completely appropriate here.)
See the documentation section on Matrix Indexing for an extended discussion.
Star Strider
Star Strider on 20 Jul 2021
As always, my pleasure!

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