Unrecognized function or variable 'qdpfun"

% qdP.m: plot of volumetric flow rate vs. dP
clear all;
dP = -18*1.01325e5; dz = 100; rho = 1e3; mu = 1e-3; L = 1500; D = 0.154; rh = 4.57e-5; % data
x0 = [5 0.001]; % initial guess (x(1)=v, x(2)=f)
x = fsolve(@qdpfun,x0,[],dP,dz,rho,mu,L,D,rh);
v = x(1); f = x(2); Q = x(1)*pi*D^2/4; % volumetric flow rate
dPf = 2*f*rho*L*v^2/D; % pressure drop due to friction loss
fprintf('Volumetric flow rate of water = %g m^3/sec\n', Q);
fprintf('Pressure drop due to friction loss = %g kPa\n', dPf/1000);

function fun = qdpfun(x,dP,dz,rho,mu,L,D,rh)
v = x(1); f = x(2); g = 9.8; Nre = D*v*rho/mu; % Reynolds number
fun = [-v^2/2 + g*dz + dP/rho + 2*f*L*v^2/D; 1/sqrt(f) + 1.7372*log(rh/3.7/D + 1.255/Nre/sqrt(f))];
end


If you'll run the code, it shows, Unrecognized function or variable 'qdpfun'. Please help in solving the error in the code above

Answer 1

[Davide Masiello]

Below, I show the right way to pass extra parameters to a function.

clear,clc

dP = -18*1.01325e5; 
dz = 100; 
rho = 1e3; 
mu = 1e-3; 
L = 1500; 
D = 0.154; 
rh = 4.57e-5;       
x0 = [5 0.001];     

x = fsolve(@(x)qdpfun(x,dP,dz,rho,mu,L,D,rh),x0);

Equation solved.

fsolve completed because the vector of function values is near zero
as measured by the value of the function tolerance, and
the problem appears regular as measured by the gradient.

v = x(1); 
f = x(2); 
Q = x(1)*pi*D^2/4; % volumetric flow rate
dPf = 2*f*rho*L*v^2/D; % pressure drop due to friction loss

fprintf('Volumetric flow rate of water = %g m^3/sec\n', Q);

Volumetric flow rate of water = 0.0610367 m^3/sec

fprintf('Pressure drop due to friction loss = %g kPa\n', dPf/1000);

Pressure drop due to friction loss = 849.219 kPa

function fun = qdpfun(x,dP,dz,rho,mu,L,D,rh)
v = x(1); f = x(2); g = 9.8; Nre = D*v*rho/mu; % Reynolds number
fun = [-v^2/2 + g*dz + dP/rho + 2*f*L*v^2/D; 1/sqrt(f) + 1.7372*log(rh/3.7/D + 1.255/Nre/sqrt(f))];
end

[Crizel Joyz Amano]

I copied your code as is and it still shows Unrecognized function or variable 'qdpfun'. I am new to MATLAB so I haven't navigated the application yet.

[Davide Masiello]

Have you copied the code in a script, saved it and then run it?

[Crizel Joyz Amano]

tried it and it worked already. thank you so much for the help!!