Not enough input arguments for bisection method function.

I have problems for determining variable "t" for "pCO2" value.

This is the function of pH:

function y = f(pH,pCO2) % Function for calculating pH (Seperate f.m file)
k1= 10 ^(-6.3);
k2= 10^(-10.3);
kw= 10^(-14);
kh= 10^(-1.46);
H=10^(-pH);
y= k1/(1e6*H)*kh*pCO2 + 2*k2*k1/ (1e6*H)*kh*pCO2 + kw/H - H;
end

This is the bisection method function to determine the pH.

function bisec %Seperate bisec.m file
i=0; % Initial condition
xl=2; % Lower limit
xu=12; % Upper limit
Ead=0.005; % Relative percent error
n=log2((xu-xl)/Ead); % Number of max iterations
n=ceil(n); % Round up to closest number

prompt = 'Set year:  ';
t = input(prompt);
pCO2 = 0.012226*(t-1983)^2+1.418542*(t-1983)+ 342.38309; % pCO2 equation with respect to years.


while f(xl)*f(xu)>0 % Setting fail condition
    disp('Bisection method will not work.'\n)
    xl=2;
    xu=12;
end

for i=1:n % Starting iterations
    
    xmid =(xl+xu)/2; % Bisection method
    
    if f(xmid)*f(xu)<0 % Setting limits
        xl = xmid;
    else
        xu = xmid;
    end
    fprintf('pH is %f for iteration %d\n',xmid,i); % Display the result
end
end

Whenever I run, this error displays:

>> bisec
Set year:  1958
Not enough input arguments.

Error in f (line 7)
y= k1/(1e6*H)*kh*pCO2 + 2*k2*k1/ (1e6*H)*kh*pCO2 + kw/H - H;

Error in bisec (line 14)
while f(xl)*f(xu)>0 % Setting fail condition
end

If I set a constant value for pCO2 in f file, like pCO2=315; and remove

prompt = 'Set year:  ';
t = input(prompt);
pCO2 = 0.012226*(t-1983)^2+1.418542*(t-1983)+ 342.38309; % pCO2 equation with respect to years.

lines from bisection file (lines 9-11), it works:

>> bisec
pH is 7.000000 for iteration 1
pH is 4.500000 for iteration 2
pH is 5.750000 for iteration 3
pH is 5.125000 for iteration 4
pH is 5.437500 for iteration 5
pH is 5.593750 for iteration 6
pH is 5.671875 for iteration 7
pH is 5.632813 for iteration 8
pH is 5.613281 for iteration 9
pH is 5.623047 for iteration 10
pH is 5.627930 for iteration 11

What should I do for this code to ask a year from the user to calculate pCO2 and determine the pH with bisection method?

Thanks.

Answer 1

[Jan]

You have defined f() with 2 input:

function y = f(pH,pCO2)

but you call it with 1 input only:

while f(xl)*f(xu)>0

I guess you want:

while f(xl, pCO2) * f(xu, pCO2) > 0 

[Turgut Ataseven]

Thank you so much, that worked well.