Why is it giving me undefined function for the slope field?

f=@(x,y)(exp(-x)-y)*(exp(-x)+2+y)
slopefield(f,[xmin,xmax],[-10,10],20)
hold on
drawode(f,[-10,10],2,3)
drawode(f,[-10,10],5,7)
hold off

[Adam Danz]

In the future, please use the { } button to format your code.

f=@(x,y)(exp(-x)-y)*(exp(-x)+2+y) 
slopefield(f,[xmin,xmax],[-10,10],20) 
hold on 
drawode(f,[-10,10],2,3) 
drawode(f,[-10,10],5,7) 
hold off

Where did you get this function slopefield? This 3rd party FEX?

If so, there's no documentation, no ratings, and that makes it difficult to know what this function is supposed to do without downloading it and opening the hood. Do you get an error when you run your function f() with the x and y inputs?

[Bish Erbas]

Make sure you have downloaded the .m file for slopefield function and placed this file into a folder that is in MATLAB path.

[Adam Danz]

I think @Bish is right that this error is due to not having access to slopefield() rather than an error associated with the nested function f(). A quick way to test that is by executing:

which ('slopefield.m')

[Natalie Haddadeen]

i did upload to matlab both files, it still giving me undefined function or variable 'f'

[Bish Erbas]

I am guessing you meant download, right? Downloading the files is not sufficient for MATLAB to recognize them as functions. You need to move or copy these files into a folder that MATLAB can recognize. Read more here: https://www.mathworks.com/help/matlab/matlab_env/what-is-the-matlab-search-path.html

[Adam Danz]

Natalie, a simple test as I mentioned already is to merely run this line of code from the command window in Matlab.

which ('slopefield.m')

If it returns, file not found then you know that the file is not on the path.

If that's the case, find the file, copy the full path to that file, then add the path like this:

addpath('C:\Users\myname\Documents\MATLAB\myfunctions')

[Brenda]

what is "myfunctions", i don't have that

[Rik]

That is an example folder. Replace it with whatever folder you are actually using to store your functions.

[David Goodmanson]

<modified>

Hi Natalie,

could the function possibly be called slope_field rather than slopefield?

[Jan]

@David Goodmanson: Breanda is not the OP.

[Torsten]

@Brenda

The path given in

addpath('C:\Users\myname\Documents\MATLAB\myfunctions')

was just an example.

Once you find the file you search for, you must add the path to this file (i.e. your path) in the way as shown above.

Answer 1

[David Goodmanson]

Hello Brenda,

As an alternative to figuring out how to get that code up and running, or as a comparison, you can run your own code:

xmin = -3; xmax = 6, delx = .3;
ymin = -6; ymax = 6, dely = .3;
[x y]= meshgrid([xmin:delx:xmax],[ymin:dely:ymax])

f=@(x,y)(exp(-x)-y).*(exp(-x)+2+y);          % change  *  to   .*
th = atan(f(x,y));
linlen = .2;                                 % line lengths
u = linlen*cos(th);             
v = linlen*sin(th);
figure(1)
quiver(x,y,u,v,0,'showarrowhead',0)
grid on
axis equal
xlabel('x')
ylabel('y')