Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

In the first part the codes work perfectly and it calculates all the forces Fp. In the second line the loop won't work, but I do the exact same thing.

Thanks for the help!

close all 
clear all 

%% Piston kracht

F1=100 %[N] 
hoekF=90
slopearm=[0:1:90]
alpha=90-hoekF+slopearm
r=25
x=20
hoeksup=asind((3*sind(135-slopearm))/(square((x^2)+(3^2)-2*x*3*cosd(135-slopearm))))
beta=90-hoeksup

syms Fp
eqn=F1*cosd(alpha)*r==Fp*cosd(beta)*x
for K = 1 : length(eqn)
  d(K) = double(vpasolve(eqn(K), Fp))
end

plot(slopearm,d)
title('Krachtverloop in bovenste piston') 

%% Scharnier krachten F2 en F3 

syms F2 
Xs=F1*sind(alpha)+d*sind(beta)-F2*sind(alpha)==0
Ys=F1*cosd(alpha)-d*cosd(beta)-F2*cosd(alpha)==0
for A = 1 : length(Xs)
  k(A) = double(vpasolve(Xs(A), F2))
end

Answer 1

[Star Strider]

The problem is that the first element of ‘Xs’:

4501354550746679/8796093022208 == 0

is not a function of ‘F2’, so it returns an empty element.

Beginning the loop at 2 (and preallocating ‘k’), iavoids that problem:

k = zeros(size(Xs));
for A = 2 : length(Xs)
    k(A) = double(vpasolve(Xs(A), F2));
end

The first element of ‘k’ is now 0.

[Xavier Croes]

Thank you very much!

[Star Strider]

As always, my pleasure!

Answer 2

[Walter Roberson]

alpha starts out 0. sind(0) is 0. Multiply by F2 and you get 0. Therefore the equation becomes independent of the variable you are trying to solve for and so vpasolve cannot find a solution and returns empty.

[Xavier Croes]

Thank you very much!!!