Error "First input argument must be a function handle." function used fzero Please help to resolve the issue. Thanks

LHS =   n(1) * (hf_0(1) + dh_CH4 ) + n(2) * (hf_0(2) + dh_O2); % I holds a double       
%function [T_ad] = usolver(dh_CH4,dh_O2,n,hf_0,dh_CO2,dh_H2O,epsilon)
n = [1,2,1,2];
hf_0 = [-74873 , 0, -39352, -241826];
f = @(x) (- n(3) * (hf_0(3) + dh_CO2(x)) - n(4) * (hf_0(4) + dh_H2O(x))) + LHS  ; % dh_CO2 & dh_H2O are functions in x 
fzero(f,1000)

Error using fzero>localFirstFcnEvalError
FZERO cannot continue because user-supplied function_handle ==> @(x)(-n(3)*(hf_0(3)+dh_CO2(x))-n(4)*(hf_0(4)+dh_H2O(x))) failed with the error below.
First input argument must be a function handle.

Answer 1

[Star Strider]

The assignment statements are out-of-order (so ‘n’ and ‘hf_0’ do not yet exist when they are assigned in ‘LHS’) and two functons and two variable values are missing.

Supply the correct functions and values values and it should actually produce a useful result —

    
%function [T_ad] = usolver(dh_CH4,dh_O2,n,hf_0,dh_CO2,dh_H2O,epsilon)

dh_CO2 = @(x) sin(x);
dh_H2O = @(x) cos(x);
dh_CH4 = 1/42;
dh_O2 = 1/42^2;

n = [1,2,1,2];
hf_0 = [-74873 , 0, -39352, -241826];
LHS =  n(1) * (hf_0(1) + dh_CH4 ) + n(2) * (hf_0(2) + dh_O2); % I holds a double   
f = @(x) (- n(3) * (hf_0(3) + dh_CO2(x)) - n(4) * (hf_0(4) + dh_H2O(x))) + LHS  ; % dh_CO2 & dh_H2O are functions in x 
fzero(f,1000)

Exiting fzero: aborting search for an interval containing a sign change
    because NaN or Inf function value encountered during search.
(Function value at -Inf is NaN.)
Check function or try again with a different starting value.

ans = NaN

.