Error: Unable to perform assignment because the left and right sides have a different number of elements.(line 25)

%chebyshev differentiation matrix 

function [D,x] = cheb(N)

if N==0,D=0;x=1;return,end 
x=cos(pi*(0:N)/N)'; 
c=[2;ones(N-1,1);2].*(-1).^(0:N)'; 
X=repmat(x,1,N+1); 
dX=X-X';
D=(c*(1./c)')./(dX+(eye(N+1))); 
D=D-diag(sum(D')); 


end

%Differentiatio matrix and initial data 
N=20; 
[D,x]=cheb(N); 
D2=D^2; 
eps=1; 
dt=min([.01,50*N^(-4)/eps]); 
t=0; 
sigma=.10;
r=.12; K=100; 
k=2*r/sigma^2; 
v=max(exp((k+1)/2)*x-exp((k-1)/2)*x,0);
t=0;

%Differentition matrix and initial data; 

%solve pde 
tmax=100;tplot=2
nplots=round(tmax/tplot)
plotgap=round(tplot/dt),dt=tplot/plotgap 
xx=-1:.025:1; vv=polyval(polyfit(x,v,N),xx); 
plotdata=[vv;zeros(nplots,length(xx))]; tdata=t; 
for i=1:nplots
    for n=1:plotgap 
        t=t+dt;v=v+dt*(eps*D2*v); 
        v(1)=exp(((k+1)/2)*x+(((k-1)/2).^2+k)*t)-exp(((k-1)/2)*x+(((k-1)/2)^2)*t);
        v(end)=0; 
    end 
    vv=polyval(polyfit(x,v,N),xx); 
    plotdata(i+1,:)=vv;tdata=[tdata;t]; 
end 
clf,subplot('position',[.1 .4 .8 .5])
mesh(xx,tdata,plotdata),grid on 
axis([-1 1 0 tmax -1 2]), 
view(-60,55),colormap([0 0 0]),xlabel x,ylabel t,zlabel u

[Walter Roberson]

Which cheb() function are you using?

.. We need to know in order to figure out what the size of D and x will be.

[Asir Tushar]

sorry, I am attaching the cheb function

Answer 1

[Walter Roberson]

Your x is a column vector of length N+1. You use all of it in the right hand side of your calculation of v(1) so the right hand side is going to have N+1 elements. You will not be able to fit that into the scalar location v(1).

[Asir Tushar]

I did not undestand fully

[Asir Tushar]

v(1) has only one scalar location whereas v(1) is computing (N+1) terms. Am I right ?

[Walter Roberson]

Yes. The part to the right creates N+1 results but v(1) is only enough room to store one result.

[Asir Tushar]

okay. thanks

[Asir Tushar]

Should I use another loop to store each results ?