I'm getting Undefined Variable Error when the variable is defined.

Here's the code in question. I'm taking inputs from another function, which calls this one. The variable p is "undefined, despite it being defined in line 10, with the error on line 13. Can anyone give some advise to fix this?

function [ p ] = ISOmax( MAXS1, MAXS2, TAB)
%Maximize ISO function

%values for consumer bids
D1 = [-.52 100];
D2 = [-.65 100];

%variable calculations
PA = 1;
p = 1;
%Production by S1
    function [Q1] = Q1 (p, MAXS1)
        Q1 = (p - MAXS1(1,2)) / MAXS1(1,1);
    end
Q1
%Production by S2
    function [Q2] = Q2 (p, MAXS2)
        Q2 = (p - MAXS2(1,2)) / MAXS2(1,1);
    end
Q2
%total production at A
    function [QA] = QA (Q1, Q2)
        QA = Q1 + Q2;
    end
QA
%Consumption by D1
    function [d1] = d1 (p)
        d1 = (p - 100) / -.52;
    end
d1
%Consumption by D2
    function [d2] = d2 (p)
        d2 = (p - 100) / -.65;
    end
d2
%total consumption at B
    function [DB] = DB (d1, d2)
        DB = d1 + d2;
    end
DB
%consumer Surpluses
    function [CS1] = CS1 (p, d1)
        CS1 = .5 * (100 - p)* d1;
    end
CS1
    function [CS2] = CS2 (p, d2)
        CS2 = .5 * (100 - p)* d2;
    end
CS2
%Supplier Surplus
    function [PS1] = PS1 (p, MAXS1, Q1)
        PS1 = .5 * (p - MAXS1(1,2)) * Q1;
    end
PS1
    function [PS2] = PS2 (p, MAXS2, Q2)
        PS2 = .5 * (p - MAXS2(1,2)) * Q2;
    end
PS2
%Benefit to consumers
    function [BB] = BB (CS1, p, d1, CS2, d2)
        BB = CS1 + p * d1 + CS2 + p * d2;
    end
BB
% Cost to Producers
    function [CA] = CA ( p, Q1, PS1, Q2, PS2)
        CA = p * Q1 - PS1 + p * Q2 - PS2;
    end
CA
%Total Welfare Formula
   function [TW] = TW (BB, CA)
        TW = BB - CA;
    end
%Negative TW Formula, for Matlab maximazation function    
    function [TWA] =TWA (TW)
        TWA = -1*TW;
    end
p = fminbnd(TWA,0,1000) 

p
end

Answer 1

[Walter Roberson]

You need to add "end" to the file, or else the file will not be interpreted as having nested functions.

[Patrick]

I only posted the first part of the code, it does have an end later.

[Walter Roberson]

Ah, I see now. You define p as being a parameter to Q1 and to Q2. When you define a variable as being a parameter to a function, the variable will not inherit from its surrounding context, and you must pass in a value for that parameter.

[Patrick]

At this time I'm not trying to pass the variable into the function, I'm defining a number of functions that are then going into a final function to calculate the maximum of a function, based off of the other functions that are a part of it.

Also, here's the error from matlab.

??? Input argument "p" is undefined.

Error in ==> ISOmax>Q1 at 13
        Q1 = (p - MAXS1(1,2)) / MAXS1(1,1);

Error in ==> ISOmax at 15
Q1

I've added in the rest of the code, if that will help.

[Walter Roberson]

Your lines

    function [Q1] = Q1 (p, MAXS1)
        Q1 = (p - MAXS1(1,2)) / MAXS1(1,1);
    end

define the function Q1 as being a function with two parameters, the first of which is named "p".

The next line in your code is

Q1

which is a call to Q1 with no parameters. The two input arguments to Q1 are then undefined, so you get an error when the code attempts to use them.

Remember, function name with no parameters is a call to the function.

Note: do not name your output parameter with the same name as the function.

Answer 2

[Star Strider]

I think I see the problem. When you call Q1 (and for that matter many of your other functions) as you do here:

%Production by S1
    function [Q1] = Q1 (p, MAXS1)
        Q1 = (p - MAXS1(1,2)) / MAXS1(1,1);
    end

you have a self-referential call,because MATLAB is getting confused by all the Q1 references. When you assign Q1 in the function, it is probably interpreting that as a call to Q1 without any arguments. I suggest you either change the name of the function:

%Production by S1
    function [Q1] = FunctionQ1 (p, MAXS1)
        Q1 = (p - MAXS1(1,2)) / MAXS1(1,1);
    end

or (probably preferably) change them all to anonymous functions, e,g,:

Q1 = @(p, MAXS1) (p - MAXS1(1,2)) / MAXS1(1,1);

along with the others.