using fsolve with matrix

I would like to calculate xeq using fzero

xeq should be a vector.

T and Y is a vector.

function ydot=Zazarian_f_5(~,x)

X=x(1); y=x(2); T=x(3);

% given & calculation

T0=325;
Ta=300;
Fa0=5;
Fb0=10;
Fi0=10;
Ca0=0.2;
Cp_a=20;
Cp_b=20;
Cp_c=20;
Cp_i=18;
alpha=0.00015;
k1=0.0002;
Ua=320;
pb=1400;
e=25000;
mc=18;
thb=2;
thi=2;
delta_Hrx=-20000;
Cp_cool=18;
r=1.987;
kc1=1000;
%calculation

k2=k1*exp((e/r)*((1/300)-(1/T)));
Kc2=kc1*exp((-delta_Hrx/r)*((1/305)-(1/T)));
CA=Ca0*(1-X)*y*(T0/T);
CB=Ca0*(1-X)*y*(T0/T);
CC=Ca0*(1+2*X)*X*y*(T0/T);
Ci=2*Ca0*y*(T0/T);
ra=-k2*((CA*CB)-((CC^2)/Kc2));

ydot(1)=(-ra)/(Fa0);
ydot(2)=(-alpha/(2*y))*(T/T0);
ydot(3)=(-delta_Hrx*ra)/(Fa0*(Cp_a+(thb*Cp_b)+(thi*Cp_i)));
ydot = ydot';

end


%%Script:

clear all

clc

y0=[0 1 325]; % why a initial pressure drop of 1
W=[0 1000];
r=1.987;
kc1=1000;
Tkc1 = 305;
T0=325;
delta_Hrx=-20000;
% X vs W
[t,y]=ode45(@Zazarian_f_5, W, y0);
Teq = y(:,3);
Y=y(:,2);
X = y(:,1);
T = T0 + (X*delta_Hrx)/(60);
% Temperature vs W
figure
plot(t, T);
%using other guys

%plot(t, y(:,3));
xlabel('catalyst weight in kg');
ylabel('Temperature');
legend('T');
title('Temperature');
% step 2 Kc -- equilibrium constant equation at a t
xo=0;
%Kc2=kc1*exp((-delta_Hrx/r)*((1/305)-(1/T)));
Ca0=0.2;

KC=kc1*exp((-delta_Hrx/r)*((1/Tkc1)-(1./Teq)));
CA=@(xeq)Ca0*(1-xeq).*Y*(T0./Teq);
CB=@(xeq)Ca0.*(1-xeq).*Y.*(T0./Teq);
CC=@(xeq)Ca0*(1+2.*xeq).*Y.*(T0./Teq);
myfun=@(xeq) CC(xeq).^2./(CA(xeq).*CB(xeq))-KC;

XEQ=fzero(myfun,xo);

Error using fzero (line 306)
FZERO cannot continue because user-supplied function_handle ==> @(xeq)CC(xeq).^2./(CA(xeq).*CB(xeq))-KC failed with the
error below.

 Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of
 rows in the second matrix. To perform elementwise multiplication, use '.*'.

Error in zzz (line 41)
XEQ=fzero(myfun,xo);
 
>> 

Answer 1

[Walter Roberson]

fzero() can only be used for functions of one variable that return scalar results.

You will need to switch to fsolve() instead of fzero()