error when writing a function

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Richard 2012-2-21

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编辑： Azzi Abdelmalek 2013-10-18

When using a function that I have written, matlab returns the error:

Undefined function or variable 'Bathymetry'
Error in import_txt (line 58)
data = Bathymetry;

I know this stated that I haven't defined that variable but I have, I can see it in the workspace. Furthermore, the script works fine if I use it normally, this error only occurs when I try to use it as a function. What could cause this error?

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Answer 1

Aurelien Queffurust 2012-2-21

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The reason is that Bathymetry variable is only known in base workspace but not in the workspace of your function (as you have already identified , see the doc for further information)

try

data =evalin('base','Bathymetry');

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Aurelien Queffurust 2012-2-21

Link for the doc about "Scope of a Variable":

http://www.mathworks.fr/help/techdoc/matlab_prog/f0-38052.html#f0-38068

Jan 2012-2-21

I'm convinced that recommending EVALIN will increase the confusion of a Matlab beginner.

@lestyn: I suggest to avoid EVAL, EVALIN and ASSIGNIN generally. It reduces the readibility and processing speed, while it increases the complexity of a program substantially, such that the debugging gets really cruel. Better use a clean input/output interface for the function.

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Answer 2

Jan 2012-2-21

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Please read the Getting Started chapters of the documentation, especially the articles about "functions" and "scripts". A function has its own workspace and sees only the variables, which have been delivered as inputs. E.g. in:

a = 23;
x = sin(0:0.1:2);

the value of a is not visible inside the sin function, as all internal variables of sin are not visible from the outside. This is a big benefit compared to scripts, which can see and overwrite the variables of the caller. The larger a script is, the more complicated is it to keep the overview and avoid overwriting variables used by the caller by accident.

So if you need the value of Bathymetry inside a function, append it to the list of input arguments.