How can I asign values to syms during a for loop

Hi there,

I'm having a problem with the sysmbolics when I try to make a for loop to then plot the function for the different values of x.

The code is the following

syms w(x,y) W(x,y) g(y) yp z Ax

assume(y,'real')

assume(yp,'real')

% Ax = 300;

% Radius

R = 50;

q = 1/3;

k = 0.04;

sigmas = 1/3*(k*x+R)^2;

% c(x)

c = R^2*(1-q)/(2*sigmas);

% Tau squared

taus = 2/3*k*(k*x+R)*Ax;

w(x,y)=sqrt(c)*exp(-y^2/(2*sigmas));

g(z) = exp(-z^2/(2*taus))/sqrt(2*pi*taus);

g(y-yp);

f(x,y,yp,Ax) = g(y-yp)*w(x,yp);

% Some limits of integration

a = -1000;

b = 1000;

% Define W as the integral of f(x,yp) dy from a to b

% W(x,Ax,y) = int(f(x,y,yp,Ax), yp, a, b);

Ax = 1;

N=Ax:Ax:10*R;

%W(x,y) = zeros(length(N),1); % Pre-allocation. not sure if needed

for i = N

x = i-1;

W(x+i,y) = int(f(x,y,yp,Ax), yp, a, b);

i = i + 1;

end

So basically in the for loop the W function will be evaluated at x+deltaX and then the integral of the function on the right hand side will have x as value. Basically if we start at x=0 and deltaX=0.1, we will have W(0.1,y)=int(g(y-yp)*w(0,yp))

Any idea how could I make it work ?

Answer 1

[Brahmadev]

Hi Raul,

I understand that you would like to evaluate the integral "W" for each step of "deltaX". This can be accomplished without using a for loop. You can replace the code after defining the limits "a" and "b" with the following code:

Fnew = subs(f, Ax, 1); % Symbolic substitution of Ax as 1
Ax = 1; % Defining the value of Ax for proper evaluation of Ax:Ax:50*R
% Calculating the integral after substituting the value for x as an array
% with steps deltaX
Fnew2 = subs(Fnew, x, Ax:Ax:10*R);
W = int(Fnew2, yp, a, b);

Also, it is not necessary to define "Ax" and "yp" as a symbolic variables in the first line.

Hope this helps.