Please explain this Octave Error Code: op1 is 1x12, op2 is 1x3 - octave

Question

Code:
function result = assess_polynomial_n(y,n)
[coeff, t, pred_accum] = fit_data(y, n);
[avg, std_dev] = compute_error(coeff,y);
[coeff1, t, pred_accum1] = fit_data(y, n+1);
[avg1, std_dev1] = compute_error(coeff1,y);
if avg1>avg
result = n;
elseif avg<0.1 && std_dev<0.1
result = n;
elseif pred_accum1.*(1)<0.0001
result = n;
else
result = 0;
end
end
***Error***
error: compute_error: operator -: nonconformant arguments (op1 is 1x12, op2 is 1x3)
error: called from
compute_error at line 11 column 17
assess_polynomial_n at line 19 column 18
__tester__.octave at line 38 column 1
Does anyone know why I could be getting this error? We're supposed to be working in MATLAB but pasting our code into Moodle which uses Octave if that clears anything up.
I also will post the functions I'm calling for reference since the error is occurring in Compute_Error. This is a part of an overall project where I was to define the functions I'm calling before creating assess_polynomial_n.
function [coeff, t, pred_accum] = fit_data(y, n)
len = length(y);
t = 10*[0:len-1];
coeff = polyfit(t, y, n);
pred_accum = polyval(coeff, t);
end
function [avg std_dev] = compute_error(x,y)
s=[];
for i=1:length(x)
error=abs(x(i)-y(i));
s=[s,error];
end
avg = mean(s);
std_dev = std(s);
end

Answer 1

The problem lies in this line of code:
[avg1, std_dev1] = compute_error(coeff1,y);
You are trying to compute the error between the original data and the coefficients of the fitted polynomial. It doesn't make sense, right?
Instead, you should compute the error between the original data and the fitted data, which is the polynomial's output at each t value. The correct code would be:
[avg1, std_dev1] = compute_error(pred_accum1,y);