Unrecognized function or variable 'qdpfun"

Question

Crizel Joyz Amano 2022-5-1

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1709340-unrecognized-function-or-variable-qdpfun

评论： Crizel Joyz Amano 2022-5-2

% 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

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Answer 1

Davide Masiello 2022-5-2

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1709340-unrecognized-function-or-variable-qdpfun#answer_955265

在 MATLAB Online 中打开

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