Undefined Variable or Function Fix?

So I have a very long code that is supposed to pull data from a .txt file (attached) and use it to run the code. When I directly import a specific .txt file, the code runs properly. However, I want to put the code into a function where I can input any .txt file name and it will run based on that file. Whenever I put it in a function, I get the error "Undefined Variable 'name of file' or function 'name of file'. I'll post the code below (it's very long but I believe the mistake is in the top several lines) if that helps, but I can't figure out why it will work in a script but not a function.

    function [ V_in, V, V_out ] = PIPE_FLOW( fname_in, units )

    if units == 'M'
        gamma = 9810;
        g = 9.81;
        rho = 1000;
        nu = 1.12e-6;
    elseif units == 'E'
        gamma = 62.4;
        g = 32.2;
        rho = 1.94;
        nu = 1.21e-5;
    end

    format shorteng;
    format compact;

    A = importdata(fname_in,'%f%f%f%f%f', ' ',1);

    n=length(A);  

    %Preallocate the variable vectors:
    P_in = zeros(1,n);
    z_in = zeros(1,n);
    D_in = zeros(1,n);
    P_out = zeros(1,n);
    z_out = zeros(1,n);
    D_out = zeros(1,n);
    K_L = zeros(1,n);
    V = zeros(1,n);
    L = zeros(1,n);
    D = zeros(1,n);
    z = zeros(1,n);
    rough = zeros(1,n);
    H_s_Turb = zeros(1,n);
    H_s_Pump = zeros(1,n);
    Element_Num_Pipe = zeros(1,n);
    Element_Num_Fitting = zeros(1,n);
    Element_Num_Turbine = zeros(1,n);
    Element_Num_Pump = zeros(1,n);
    inlet_i = 0;
    fitting_i = 0;
    turbine_i = 0;
    pipe_i = 0;
    pump_i = 0;

        for i = 1:2:n-1
            line_desc = A{i};
            line_data = str2num(A{i+1});

    % For each pair of input lines, put data directly into relevant
    % variable vector to store the data

    % if line_desc = 'inlet', then store variables P_in, z_in and D_in
    % if line_desc = 'pipe', store variables in relevant useful locations for
    % later use.

           switch line_desc
               case 'inlet'
                    inlet_i = inlet_i + 1;
                    P_in(inlet_i) = line_data(1);
                    z_in(inlet_i) = line_data(2);
                    D_in(inlet_i) = line_data(3);
               case 'exit'
                    P_out(inlet_i) = line_data(1);
                    z_out(inlet_i) = line_data(2);
                    D_out(inlet_i) = line_data(3);
               case 'fitting'
                    fitting_i = fitting_i + 1;
                    K_L(fitting_i) = line_data(1);
                    V(fitting_i) = line_data(2);
                    Element_Num_Fitting(fitting_i) = line_data(3);
               case 'pipe'
                   pipe_i = pipe_i + 1;
                   L(pipe_i) = line_data(1);
                   D(pipe_i) = line_data(2);
                   rough(pipe_i) = line_data(3);
                   z(pipe_i) = line_data(4);
                   Element_Num_Pipe(pipe_i) = line_data(5);
               case 'pump'
                   pump_i = pump_i + 1;
                   H_s_Pump(pump_i) = line_data(1);
                   Element_Num_Pump(pump_i) = line_data(2);
               case 'turbine'
                   turbine_i = turbine_i + 1;
                   H_s_Turb(turbine_i) = line_data(1);
                   Element_Num_Turbine(turbine_i) = line_data(2);
           end

        end

    %Remove the excess zeros from the end of each variable vector:
    P_in = P_in(1);
    z_in = z_in(1);
    D_in = D_in(1);
    P_out = P_out(1);
    z_out = z_out(1);
    D_out = D_out(1);
    K_L = K_L(1:fitting_i);
    V = V(1:fitting_i);
    Element_Num_Pipe = Element_Num_Pipe(1:pipe_i);
    Element_Num_Pump = Element_Num_Pump(1:pump_i);
    Element_Num_Turbine = Element_Num_Turbine(1:turbine_i);
    Element_Num_Fitting = Element_Num_Fitting(1:fitting_i);
    L = L(1:pipe_i);
    D = D(1:pipe_i);
    z = z(1:pipe_i);
    rough = rough(1:pipe_i);
    H_s_Turb = H_s_Turb(1:turbine_i);
    H_s_Pump = H_s_Pump(1:pump_i);
    H_s = H_s_Turb(1) + H_s_Pump(1);

    %Reference Variables:
    D_1 = D(1);
    g = 9.81;
    gamma = 9810;
    nu = 1.12e-6;

    %Guess f:
    f_g_1 = 0.025;

    %Energy Equation:
    Num = (2*g)*((P_out-P_in)/gamma+z_out-z_in-H_s);
    Denom_guess = ((D_1./D_in).^4)-((D_1./D_out).^4)-f_g_1.*(L./D).*(D_1^4./D.^4)-K_L.*(D_1^4./D.^4);
    Vref = sqrt((Num./Denom_guess));

    V_1_guess = Vref(1);
    rough_1 = rough(1);
    rel_rough = (rough_1/D_1);

    %Find a Reynolds Number based on the guessed f:
    Re = ((V_1_guess*D_1)/nu);
    %Guess f:
    if 0 < Re && Re < 2100;
        f_1_actual = 64/Re; 
    elseif Re > 4000
         f_g_2 = 0.025;        %New friction factor guess
        while Re > 4000; 
        f_1_actual = ((-2*log10((rel_rough/3.7)+(2.5/(Re*(sqrt(f_g_2))))))^-2);
        if abs(f_g_2 - f_1_actual) < 10^-5;
            break
        end
        f_g_2 = f_1_actual;
        end
    else 
        warning('Transitional Flow - Friction Factor cannot be found');
    end

    Denom_Actual = ((D_1./D_in).^4)-((D_1./D_out).^4)-f_g_1.*(L./D).*(D_1^4./D.^4)-K_L.*(D_1^4./D.^4);

    V_final =  sqrt((Num./Denom_Actual));

    %Graphing Total Head:
    H_L = (V_final./D).*(K_L);
    Head_Total = H_s_Pump + H_s_Turb + H_L;
    plot(Head_Total);
    title('Graph of Total Head from inlet to exit');

    V_in = V_final(1);
    b = length(V_final);
    V_out = V_final(b);

Running the code returns this error message:

Undefined variable "Final_Data" or function "Final_Data.txt".

[Image Analyst]

Nowhere in your code is either Fix or fix mentioned. Attach the text file if you want us to try your code and try to help you. And please post the entire error message ( ALL the red text, not a paraphrased or small snippet from it like you did).

[Image Analyst]

I don't get that error at all. I get

Error using importdata (line 225)
Unable to load file.
Use TEXTSCAN or FREAD for more complex formats.

Error in test1 (line 20)
A = importdata(fname_in,'%f%f%f%f%f', ' ',1);
Caused by:
    Error using textscan
    Name-value pair arguments must come in pairs.

Final_Data.txt is this:

inlet
0, -0.25, 2
exit
0, 400, 0.5
fitting
10, 1, 4
pipe
5, 2, 0.00015, 0, 1
pipe
10012.5, 0.5, 0.01, 500, 2
pipe
1005, 3, 0.01, 400, 3
pump
800, 4
turbine
-150, 5

With strings interleaved with lines of a varying numbers of numbers. Like the actual error message said, you're going to have to do some other kind of reader for it. I'd probably write my own. Can you do that? Do you know that the numbers for each category are constant? Like inlet will always have 3 numbers after it and pump will always have 2 numbers after it? Or can they vary?

[Neil Solan]

The numbers for each category remain constant. I don't understand why we would get two different errors though..

[Jan]

@Neil: Please post the complete error message. It will reveal immediately the location of the problem.

[Neil Solan]

This is what my command window looks like when I run the function:

>> PIPE_FLOW(Final_Data.txt,M)
Undefined variable "Final_Data" or function "Final_Data.txt". 
>>

Answer 1

[Star Strider]

Use single quotes around the file name:

FileName = 'Final_Data.txt';
PIPE_FLOW(FileName,M);