How to pass an output from a function to be processed in another function

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Monty Ramadhan on 31 Oct 2014

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Commented: Star Strider on 4 Nov 2014

So i have a function that inputs coordinates and plots a line

 function linetranslation(xa,ya,xb,yb)
if nargin == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
  
end
clf;
hold on;
axis([-10 10 -10 10]);
if xa==xb
   if ya<yb
      for yi=ya:0.01:yb;
    xi=yi+xa-yi;
    plot(xi,yi);    
      end
   else
      for yi=ya:-0.01:yb;
    xi=yi+xa-yi;
    plot(xi,yi);
      end
   end
else
   m=(yb-ya)/(xb-xa);
   if xa<xb
      for xi=xa:0.01:xb;
          yi=m*(xi-xa)+ya; 
          plot(xi,yi);
      end
   else
      for xi=xa:-0.01:xb;
          yi=m*(xi-xa)+ya;
          plot(xi,yi);
      end
   end
end
end

the question is how can i pass xi & yi to another function that processes it further

a little idea here, i have tried adding to the first function

function [xi, yi] = linetranslation(xa,ya,xb,yb)

and adding the code below

 function Translate(x,y)
>>>here [xi , yi] = linetranslation(xa,ya,xb,yb);
if nargin == 0
    % Check the number of input arguments (nargin)
    x  = input('Translate X: ');
    y  = input('Translate Y: ');
 end
 hold on;
 axescenter
 axis([-10 10 -10 10]);
 plot(xi+x,yi+y);

but it returns xa undefined, on the other hand i need xi and yi to be passed

thanks in advance

UPDATE

i have tried putting

[xi,yi] = translasigaris;

below

function translate(x,y)

but

 if nargin == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
  
end

returns as an infinite loop.

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Accepted Answer

Star Strider on 31 Oct 2014

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https://nl.mathworks.com/matlabcentral/answers/160776-how-to-pass-an-output-from-a-function-to-be-processed-in-another-function#answer_157262

If you want to make ‘xi’ and ‘yi’ available to other functions, the easiest way is to have your ‘linetranslation’ function output them.

Change your original function statement to:

function [xi,yi] = linetranslation(xa,ya,xb,yb)

When you then call it such as in this statement:

[xi,yi] = linetranslation(xa,ya,xb,yb);

‘xi’ and ‘yi’ (by whatever variable names you want to assign them to) will be available in your workspace.

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Star Strider on 31 Oct 2014

If you don’t supply your function with any input arguments, the nargin function will always evaluate to zero. Nothing you can do inside the function will change that.

One way around that would be to have another if block:

if nargin == 0
    argnr = 0;
end
if argnr == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
    argnr = 1;
end

However I would completely delete this if block:

if nargin == 0
    xa = input('First X Coordinate  : ');
    ya = input('First Y Coordinate  : ');
    xb = input('Second X Coordinate : ');
    yb = input('Second Y Coordinate : ');
end

First, because anything you enter there is going to overwrite whatever you pass as arguments to your function, and...

Second, because MATLAB will throw a ‘not enough input arguments’ error if you don’t pass all of them and you don’t have a nargin check.

The solution is to:

Delete the current if block,
Pass all the arguments to the function in your script,
Return the arguments you want as your function outputs.

Monty Ramadhan on 1 Nov 2014

Edited: Monty Ramadhan on 1 Nov 2014

first of all thankyou for helping me and here's my 'linetranslation' code

 function [xi,yi] = linetranslation() 
 dlg_title = 'Enter Coordinates:';
prompt = {'First X Coordinate:','First Y Coordinate:','Second X Coordinate:','Second Y Coordinate:'};
coords = inputdlg(prompt, dlg_title,[1 45; 1 45; 1 45; 1 45]);
[xa,ya,xb,yb] = coords{:};
xa = str2num(xa);
ya = str2num(ya);
xb = str2num(xb);
yb = str2num(yb);
 clf;
hold on;
axis([-10 10 -10 10]);
if xa==xb
   if ya<yb
      for yi=ya:0.01:yb;
    xi=yi+xa-yi;
    plot(xi,yi);
      end
   else
      for yi=ya:-0.01:yb;
    xi=yi+xa-yi;    
    plot(xi,yi);
      end
   end
else
   m=(yb-ya)/(xb-xa);
   if xa<xb
      for xi=xa:0.01:xb;
      yi=m*(xi-xa)+ya; 
    plot(xi,yi);   
    plot(xi,yi);    
      end
   else
      for xi=xa:-0.01:xb;
      yi=m*(xi-xa)+ya;
    plot(xi,yi);    
    plot(xi,yi); 
      end
   end
end
axescenter
translate

and this is my 'translate' function

 function translate(x,y)
 [xi,yi] = linetranslation();
 dlg_title = 'Enter Coordinates:';
 prompt = {'Translate X:','Translate Y:'};
 coords = inputdlg(prompt, dlg_title,[1 45; 1 45]);
 [x,y] = coords{:};
 hold on;
 axescenter
 axis([-10 10 -10 10]);
 plot(xi+x,yi+y);

the code axescenter refers it to this file here

axescenter

Monty Ramadhan on 2 Nov 2014

thanks!, i've modified my code so that the function 'linetranslation' plots 'xi' and 'yi' and plot 'xj' and 'yj' which is

 xj=xi+x;
 yj=yi+y;

As you suggested i nested 'translate' within 'linetranslation' and share the variables 'xj' and 'yj', now it plots 2 line from 'linetranslation', after plotting the lines i've modified it to call 'translate' and calling another input dialogue inside the function.

What i hope to achieve now is that the user could translate the second line from the 'linetranslation' function which is 'xj' and 'yj', this is my modified code in one m file.

The function does not returns any errors, but the problem is that function 'translate' doesn't plot a new line in the figure after executed, please review my code and thanks in advance, i think i might have made a stupid mistake somewhere

 function [xj,yj] = linetranslation()
 dlg_title = 'Enter Coordinates:';
 prompt = {'First X Coordinate:','First Y Coordinate:','Second X   Coordinate:','Second Y Coordinate:','X Translation','Y Translation'};
 coords = inputdlg(prompt, dlg_title,[1 45; 1 45; 1 45; 1 45; 1 45; 1 45]);
 [xa,ya,xb,yb,x,y] = coords{:};
 xa = str2num(xa);
 ya = str2num(ya);
 xb = str2num(xb);
 yb = str2num(yb);
 x  = str2num(x);
 y  = str2num(y);
 clf;
 axescenter
 hold on;
 axis([-10 10 -10 10]);
 if xa==xb
   if ya<yb
      for yi=ya:0.01:yb;
    xi=yi+xa-yi;
      xj=xi+x;
      yj=yi+y;
    plot(xi,yi);
    plot(xj,yj,'r');
      end
   else
      for yi=ya:-0.01:yb;
    xi=yi+xa-yi;
    xj=xi+x;
    yj=yi+y;    
    plot(xi,yi);
    plot(xj,yj,'r');
      end
   end
 else
   m=(yb-ya)/(xb-xa);
   if xa<xb
      for xi=xa:0.01:xb;
      yi=m*(xi-xa)+ya;
    xj=xi+x;
    yj=yi+y;    
    plot(xi,yi);
    plot(xj,yj,'r');
      end
   else
      for xi=xa:-0.01:xb;
      yi=m*(xi-xa)+ya;
    xj=xi+x;
    yj=yi+y;    
    plot(xi,yi);
    plot(xj,yj,'r');
      end
   end
 end
 function translate()
 dlg_title = 'Enter Coordinates:';
 prompt = {'Translate X:','Translate Y:'};
 coords = inputdlg(prompt, dlg_title,[1 45; 1 45]);
 [a,b] = coords{:};
 a = str2num(a);
 b = str2num(b);
 hold on;
 axescenter
 axis([-10 10 -10 10]);
 plot(xj+a,yj+b);
 end
 translate(xj,yj);
 end

Monty Ramadhan on 4 Nov 2014

The original code was intended just to plot a line in matlab, since i've found it that way and it works fine, i didn't bother to change it a bit, but since you've mentioned it, i've applied it to my code, and it works fine!, so thankyou once again. Yes 'xi' and 'yi' are translation functions, but the slanted line it plotted was not what i intend my application to plot, but thanks to your guide and patience i have achieved what i wanted.

What i wanted to achieve is to transform again the line that i've transformed and plotted , and i think i've achieved it, i have tested it and haven't found any bugs yet, if it's not trouble some i would like you to test the code, it's a fully running code, please tell me of flaws and bugs that you found.

Once again, Thankyou.

Star Strider on 4 Nov 2014

My pleasure!

If your code does what you want and you’re happy with it, that works for me!

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