Function input
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Hello everyone,
I know this is simple but I just can't figure it out by myself now.
I'm trying to create a function integrator, which asks the user to type the function to be integrated. I tried to use
g = input ('Enter function to be integrated: ')
f = @(x) g;
but MATLAB refuses it with Undefined function or variable 'x'. But how can we define x before so that f wouldn't get immediately evaluated?
Thanks a lot in adavnce!
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Answers (2)
per isakson
on 12 May 2012
Try
string_input_by_user = input( .....
string_input_by_user = 'sin';
foo = str2func( ['@(x)', string_input_by_user, '(x)' ] );
or better
foo = str2func( ['@', string_input_by_user ] );
these two variants work
>> foo(4)
ans =
-0.7568
--- 2010-05-13 ---
Divide and conquer. One thing at a time. What exactly does the user input? Assume the user inputs the tree letter string "sin". Thus, the value of
string_input_by_user
is
'sin'
Then you can create a function_handle
foo = str2func( ['@', string_input_by_user ] );
and make a test
>> foo(pi/2)
ans =
1
>> foo([ 0 : pi/4 : pi+eps] )
ans =
0 0.7071 1.0000 0.7071 0.0000
If the user inputs the six letter string "sin(x)" it's a bit more tricky. You can create a function_handle
foo = str2func( ['@(x)', string_input_by_user ] );
The problem is that the user might input "sin(y)".
Expression
In Matlab "47*x" is an expression not a function. Make your code work with functions first. Then return to expressions.
The Question, Increasing of speed in numerical calculation, shows how to use expressions. However, there is some noise.
btw. Do you step through the code with the debugger and inspect the value of the variable?
4 Comments
mohammad reza
on 12 Jul 2016
now that you have got a user defined function, how can u integrate the function in the script? (with out limit)
1 Comment
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