如何摆脱这个MATLAB错误？ “在赋值A（I）= B中，B和I中的元素数必须相同。”

Question

I keep getting this error for the b array below

A = ones(numTrials, 2*numDOFs);
b = ones(numTrials, 1);

k = 2;
for i = 2:numSubjects
    for j = 1:numTrials
        A(k,:) = cat(2,subject(i).trial(j).torque_integral, subject(i).trial(j).work_integral); 
        b(k) = [subject(i).trial(j).E - subject(i).trial(j).B - sum(subject(i).trial(j).work_integral)];        
        k = k + 1;
    end
end

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I tested each component of the creation of the b array (subject(i).trial(j).E, etc.) and they are all scalar values. So I should be able to add/subtract them then assign them to an index in the preallocated b array. A simple dummy version would look like this:

c = ones(4,1)

c =

 1
 1
 1
 1

c(3) = 3

c =

 1
 1
 3
 1

---

So what am I missing here? Thanks!

Answer 1

You should probably print out the size of every element that goes into the assignments, and your problem will solve itself;

size(cat(2,subject(i).trial(j).torque_integral, subject(i).trial(j).work_integral))
size([subject(i).trial(j).E - subject(i).trial(j).B - sum(subject(i).trial(j).work_integral)])

Note - I am leaving off the trailing ; in the above, which causes the value to be output to the console; also, your assignment to B has [] around it, as though you are trying to create a vector. If it's truly a single element there is no need for that...