How to get fzero with 2 variables in array?

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I want to get the x value for each y and alpha in array. But I got error like this
Error using fzero (line 274)
Function values at the interval endpoints must differ in sign.
Error in Term_Paper (line 14)
x(i)=fzero(@(y)dot(tp,fx(x)),[0.15 1]);
How to solve this?
xin=0.2; xout=0.1; Pr=0.3; qf=1;
%For Cross-Flow Module (CF)
%Calculating x
fx=@(x) ((1+((x+Pr).*(alpha-1))-((((1+((x+Pr).*(alpha-1))).^2)-(4.*alpha.*(alpha-1).*x.*Pr)).^0.5))/(2.*Pr.*(alpha-1)))-y;
for i=1:length(x)
x(i)=fzero(@(y)dot(tp,fx(x)),[0.15 1]);

Accepted Answer

Walter Roberson
Walter Roberson on 8 Dec 2021
I'm trying to solve fzero for each value of x in an array, and I get theis error:
Don't Do That.
fzero() is defined as only accepting scalar equations of one variable. It cannot in itself be used to solve at multiple x values simultaneously
You need to loop through the different alpha and y values. Your code would produce one output for each alpha and each y, so you need to output a 2D grid -- unless, that is, you intend each of those alpha values to be matched with a corresponding y value (as you have 11 of each): in that case you would only need a a vector output for each fzero system
arrayfun(@(ALPHA, Y) fzero(@(x) ((1+((x+Pr).*(ALPHA-1))-((((1+((x+Pr).*(ALPHA-1))).^2)-(4.*ALPHA.*(ALPHA-1).*x.*Pr)).^0.5))/(2.*Pr.*(ALPHA-1)))-Y), alpha, y)

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