Variables in a Matrix unable to be called

Hello,

I really need help. I am supposed to solve a triadagonal matrix that I populate with the code to follow. However I can use a matrix solver to solve the equation. For some reason I am unable to call the variables I assigned each matrix spot of the flux. So I can not back calculate as I had planned. If anyone could help I would greatly appreicate it.

Cheers.

clc;

clear all;

%Initial conditions

cellNum=10; %Number of cells

a = 10; %Width of slab (cm)

D =0.3733; %Diffusion coeffecient (cm)

sigA =0.0158; %Absorbption cross section (1/cm)

sigS =0.0158; %Scatt cross section (1/cm)

sigT =0.0158; %Total cross section (1/cm)

Source = 1; % source strength (neutrons/(cm3*s))

dx =a/cellNum; % Cell width

%flux matrix production and initial guess

flux = sym('a', [1 cellNum]);

%for i =1:cellNum

%flux(i)=sym('a');

%end

%Right Boundary Reflecting -[D d_flux/dx] = 0

B(1)=0;

A(1)=sigA;

%Left Boundary Condition

flux(cellNum)=0;

A(cellNum)=(2*D/dx^2+sigA);

%Middle Boundary conditions

for i=2:cellNum-1

C(i)=-D/dx^2;

B(i)=-D/dx^2;

A(i)=2*D/dx^2+sigA;

end

M = diag(A.*ones(1,cellNum)) + diag(B.*ones(1,cellNum-1),1) + diag(C.*ones(1,cellNum-1),-1);

Q = flux.*M;

Z=sum(Q,2);

for i=1:cellNum-1;

flux(cellNum-i)=solve(Z(cellNum-i)==1,flux(cellNum-i));

end

Answer 1

[Sibi]

clc;clear all;cellNum=10;
a = 10; %Width of slab (cm)
D =0.3733; %Diffusion coeffecient (cm)
sigA =0.0158; %Absorbption cross section (1/cm)
sigS =0.0158; %Scatt cross section (1/cm)
sigT =0.0158; %Total cross section (1/cm)
Source = 1;    % source strength (neutrons/(cm3*s))
dx =a/cellNum; % Cell width
flux = sym('a', [1 cellNum]);
for i =1:cellNum
    flux(i)=sym('a');
end
%Right Boundary Reflecting -[D d_flux/dx] = 0
B(1)=0;
A(1)=sigA;
%Left Boundary Condition
flux(cellNum)=0;
A(cellNum)=(2*D/dx^2+sigA);
%Middle Boundary conditions     
for i=2:cellNum-1
   C(i)=-D/dx^2;
    B(i)=-D/dx^2;
    A(i)=2*D/dx^2+sigA;
end
M = diag(A.*ones(1,cellNum)) + diag(B.*ones(1,cellNum-1),1) + diag(C.*ones(1,cellNum-1),-1);
Q = flux.*M;
Z=sum(Q,2);
for i=1:cellNum-1;   
flux(cellNum-i)=solve(Z(cellNum-i)==1,flux(cellNum-i));
end
flux(1:end)
round(flux,4)

what do you mean you cant call the values in matrix? i think its working.

if you have an inital flux and dont want to change your inital flux, then you just need to change last few lines as

for i=1:cellNum-1;   
fluxnew(cellNum-i)=solve(Z(cellNum-i)==1,flux(cellNum-i));
end