evaluate expression

      I have equation y=x*exp( (1-y)/(A*y)*B ) where A nd B constants in my program. I have a vector values for x. How can I evaluate y to plot y versus x ?

Answer 1

[Andrei Bobrov]

ezplot(['y-x*exp( (1-y)/(' num2str(A) '*y)*' num2str(B) ')'],[x(1) x(end)])

more

 As = ...; 
 Bs = ...;
 y = zeros(size(x));
 for j = 1:length(x)
    y(j) = fzero(@(y)y-x(j).*exp( (1-y)./(As*y)*Bs ),1);
 end
 plot(x,y);

[John D'Errico]

It is generally not a good idea to convert the numeric values into strings to then pass into ezplot. This loses precision. Far, far better is to use an anonymous function here.

[omnia]

Thank you alot

Answer 2

[Andrew Newell]

It would be simpler to provide y and solve for x:

y = -1:0.01:1;
x = y.*exp(- (1-y)./(A*y)*B );

In plotting this, you have to be careful because x goes to Inf or -Inf as y approaches zero from below:

I = y < 0 & abs(x) < 10;
plot(x(I),y(I))
hold on
I = y > 0 & abs(x) < 10;
plot(x(I),y(I))

[omnia]

yes I know it is easier to provide y and solve for x, but I don't have y. The input to my file is x values.