Hello, I am trying to create a GUI that plots data supplied using a function i have in a separate m-file

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ragheed idrees 2019-6-8

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https://ww2.mathworks.cn/matlabcentral/answers/466082-hello-i-am-trying-to-create-a-gui-that-plots-data-supplied-using-a-function-i-have-in-a-separate-m

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this is what i got so far under the plot button in the GUI

Q = str2num(get(handles.Qbox,'String'));
L = str2num(get(handles.Lbox,'String'));
P1 = str2num(get(handles.P1box,'String'));
H = str2num(get(handles.Qbox,'String'));
global AX;                                                           
AX = handles.axes1;
SizingGasPipes(Q,P1,L,H,Case,Unit);
grid on

and here is the rest of my code

function [D,P2,d] = SizingGasPipes(Q,P1,L,H,Case,Unit)
%This function computes the pipe size required to keep the pressure drop 
%within an acceptable range for a specified capacity (cubic feet per hour 
%or BTU per hour) and upstream pressure P1
global AX;
axes(AX);
%Giving error when user supplies an illegal value
if H>P1
    clc
    disp('Error: Pressure drop cannot be less than downstream pressure')
    P2=('Error');
    D=('Error');
    return
elseif Q<=0
    clc
    disp('Error: Flow rate cannot equal zero or negative');
    P2=('Error');
    D=('Error');
elseif P1<=0
    clc
    disp('Error: Downstream pressure cannot equal zero or negative');
    P2=('Error');
    D=('Error');
    return
elseif L<=0
     clc
    disp('Error: Length of pipe cannot equal zero or negative');
    P2=('Error');
    D=('Error');
    return
end
%Calculate inlet pressure
P1a = P1 +14.7;
P2a = P1a + H/27.7;
%generate 100 numbers from 0 to Q
switch Case %seperate Natural Gas from Propane values    
    case 'NG'   %Case 1 is Natural Gas
        Cr = 0.6094;
        Y = 0.9992;
        btucfh=1040;
    case 'PP'   %case 2 is Propane
        Cr = 1.2462;
        Y = 0.991;
        btucfh=2500;
    otherwise
        disp('Gas type invalid')
end
switch Unit %Deciding the units to convert the Q accordingly    
    case 'CFH'
    xscale=1;
       xtext = 'Capacity is in cubic feet per hour';
    case 'BTU'
       xscale= btucfh/1000;
       xtext = 'Capacity is in British Themal Units per hour';
    otherwise 
        disp('Units invalid')
end
%changing Q according to units supplied
Qc=Q/xscale;
%Calculations for the capacity of natural gas or propane piping
D = zeros(1,1000);
xx = linspace(0,2*Qc,1000);
for ii = 1:1000
    Qc(ii)=ii+1;
if H < 1.5           %Pressure drop is less than 1.5 psi
            D(ii) = (Qc(ii).^0.381)/(19.17*(H./(Cr.*L))^0.206);
                 
        elseif H >= 1.5     %Pressure drop is greater than or equal to 1.5 psi
            D(ii) = (Qc(ii).^0.381)/(18.93*((P1a.^2-P2a.^2).*Y./Cr.*L)^0.206); 
end
end
plot(xx,D)
end