MATLAB: I did not understand the error which is called ‘Error using symengine: Array sizes must match.’ What should i do

defining syms over and over againsymengine

x1=0.2232585;
x2=0.2232585;
iteration=0;
while true
    
    iteration=iteration+1;
    syms x1s x2s t
    func=(x2s-x1s^2)^2+(1-x1s)^2;
    dif_x1=diff(func,x1s);
    dif_x2=diff(func,x2s);    
    grad_x1_temp=vpa(subs(dif_x1,x1));
    grad_x1=vpa(subs(grad_x1_temp,x2));
    grad_x2_temp=vpa(subs(dif_x2,x2));
    grad_x2=vpa(subs(grad_x2_temp,x1));
    tx1_temp=subs(dif_x1,x1-grad_x1*t);
    tx1=subs(tx1_temp,x2s,x2-grad_x2*t);
    tx2_temp=subs(dif_x2,x2s,x2-grad_x2*t);
    tx2=subs(tx2_temp,x1s,x1-grad_x1*t);
    eqn=tx1*grad_x1+tx2*grad_x2;
    a=solve(eqn,t,'Real',true);
    val_temp=vpa(subs(func,x1s,x1));
    val=vpa(subs(val_temp,x2s,x2));
    x1=x1-grad_x1*a;
    x2=x2-grad_x2*a;
    val_temp_end=vpa(subs(func,x1s,x1));
    val_end=vpa(subs(val_temp_end,x2s,x2));
        if(val_end>val)
            break;
        end
        
end
iteration
Error using symengine
Array sizes must match.
Error in sym/privBinaryOp (line 1013)
Csym = mupadmex(op,args{1}.s,
args{2}.s, varargin{:});
Error in – (line 7)
X = privBinaryOp(A, B,
'symobj::zipWithImplicitExpansion',
'_subtract');
Error in THE5 (line 26)
tx1_temp=subs(dif_x1,x1-grad_x1*t);
I keep getting these errors anyone has a clue?

Best Answer

Hi Mert,
The Probelm arises in the 3rd iteration. In the 3rd Iteration x1 is size of 3x1 symfun and grad_x1 is size of 9x1 .
so the line 
tx1_temp=subs(dif_x1,x1-grad_x1*t);
is throwing error as MATLAB is not able to resolve "x1- grad_x1*t".
So make sure both x1 and grad_x1 are of same size or "x1-grad_x1*t" should make sense like we can subtract 2x2 matrix from 1x2 like this :
syms x1 x2
p = [x1,x2;x2,x1];
t = [x1,x1] - p;
Thanks,
Deepak
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