How to solve parameter values from a system of non-linear equations in matlab

Question

I'm a beginner in matlab. I have three non-linear equations

spdratio_fw = ( 1 + afw*(vc_fw)^b);
spdratio_pa = ( 1 + aps*(vc_pa)^b);
ind =  (ddhv_fw*( 1 + afw*(vc_fw)^b) - ddhv_pa*( 1 + aps*(vc_pa)^b))/(ddhv_fw + ddhv_pa) ;

from the above three equations i have to solve for afw, aps and b.

so i wrote the commands and saved in trial.m

function F = trial(Y)
afw = Y(1);
aps = Y(2);
b = Y(3);
spdratio_fw = 1.329;
spdratio_pa = 1.168;
ind = 1.312;
vc_fw = 3.2;
vc_pa = 0.76;
ddhv_fw = 20776.82;
ddhv_pa = 2536.54;

fA = spdratio_fw - ( 1 + afw*(vc_fw)^b);
fB = spdratio_pa - ( 1 + aps*(vc_pa)^b);
fC = ind - (ddhv_fw*( 1 + afw*(vc_fw)^b) - ddhv_pa*( 1 + aps*(vc_pa)^b))/(ddhv_fw + ddhv_pa) ;

F = [fA; fB; fC];



end

and after that i ran a script

afw0 = 0.15; aps0 = 0.15; b0 = 1; 
Y0 = [afw0; aps0; b0];
Y = fsolve(@trial, Y0);
result;

but the error i received:

??? Maximum recursion limit of 500 reached. Use set(0,'RecursionLimit',N) to change the limit. Be aware that exceeding your available stack space can crash MATLAB and/or your computer.

Error in ==> optimget

Caused by: Failure in initial user-supplied objective function evaluation. FSOLVE cannot continue.

i gave the command :

trial

and the error is:

??? Input argument "Y" is undefined.

Error in ==> trial at 2
afw = Y(1);

I have no idea on how to fix it.

Why and how do you think your problem is different? Show what you've tried, so that we have a starting point to help out. — Cecilia

Daniel Daniel · Accepted Answer · 2015-03-29T20:13:09

You have a function trail which calls fsolve with input a handle to trail. That's an infinite recursion loop. The last three lines should not be part of trail.m

Besides trail is a function, you cant call it as trail, you have to pass the parameter Y, for example trail(Y0)

How to solve parameter values from a system of non-linear equations in matlab

1 Answers