Unable to perform assignment because the left and right sides have a different number of elements. Can anyone help me with this?

clear all
clc
%boundary condition
x1=[0 0.0069 0.1565 0.3396 0.4666 0.6004 0.7021 0.8286 0.8868 0.9165 0.9561 0.9840 1.0];
P=[57.52 58.2 126 175.3 189.5 224.3 236 250 259 261.11 264.45 266.53 271];
% length(x1)
% length(P)
p=polyfit(x1,P,4);
dpdx=polyder(p);
y10=9.029e-5;
I0=0;
xspan=[1e-5 0.99999];
[x,y]=ode15s(@gibbs,xspan,[y10 I0])
plot(x,y)
function dy= gibbs(x,y)
x1=[0 0.0069 0.1565 0.3396 0.4666 0.6004 0.7021 0.8286 0.8868 0.9165 0.9561 0.9840 1.0];
P=[57.52 58.2 126 175.3 189.5 224.3 236 250 259 261.11 264.45 266.53 271];
p=polyfit(x1,P,4);
dpdx=polyder(p);
dy=zeros(2,1);
P1v=271;
P2v=57.52
Pr=p(1,1)*x^4+p(1,2)*x^3+p(1,3)*x^2+p(1,4)*x+p(1,5);
dP=(dpdx(1,1)*x^3+dpdx(1,2)*x^2+dpdx(1,3)*x+dpdx(1,4));
% dP=-1447.1*x^3+2724.2*x^2-1780.8*x+556.29;
% Pr=-361.764*x^4+908.0529*x^3-890.3941*x^2+556.2994*x+56.2611;
dy(1)=(y.*(1-y)./(y-x)).*(dP)./(Pr) ;
dy(2)=log((y.*Pr)./(x.*P1v))-log((1-y).*Pr./((1-x).*P2v));
end

[madhan ravi]

the problem arises in dy(2)

Answer 1

[Luna]

Hi,

Change like below:

dy=zeros(2,2);

dy(:,1)=(y.*(1-y)./(y-x)).*(dP)./(Pr) ;
dy(:,2)=log((y.*Pr)./(x.*P1v))-log((1-y).*Pr./((1-x).*P2v));

[Md Mezbah Uddin]

Now it says 'GIBBS must return a column vector'

[Luna]

Your code in below gives 2x1 vectors.

(y.*(1-y)./(y-x)).*(dP)./(Pr)  % result [11.1169 0]'
log((y.*Pr)./(x.*P1v))-log((1-y).*Pr./((1-x).*P2v)) % result [0.6505 -Inf]'

And you are trying to assign them dy(1) and dy(2) which represents just first and second element of a double array.

Which values you are going to use?

[Md Mezbah Uddin]

thanks for the help