# Substituting and evaluating function

3 vues (au cours des 30 derniers jours)
Gavin Seddon le 13 Sep 2017
Commenté : Star Strider le 13 Nov 2017
I have attempted to substitute the X variable into my function and evaluate it. This is the result. If it is not possible please tell me and I will find a difference method?
>> subs der(140,x);
Warning: Support of character vectors that are not valid variable names or define
a number will be removed in a future release. To create symbolic expressions,
first create symbolic variables and then use operations on them.
> In sym>convertExpression (line 1586)
In sym>convertChar (line 1491)
In sym (line 199)
In subs (line 66)
>> eval der
der =
(13459*cos((313*x)/200 - 1689/2000))/25 + (42471*cos((1573*x)/1000 + 1153/500))/80 + (937443*cos((1849*x)/2500 + 441/250))/62500
GS.
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Stephen23 le 13 Sep 2017
What is der? Is it symbolic, or is it a simple function handle?
Gavin Seddon le 13 Sep 2017
Hello, der is the symbolic function that is the result of dIff fx.

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### Réponse acceptée

Star Strider le 13 Sep 2017
Try this (in R2012a and later):
syms x
X = sym(140);
der(x) = (13459*cos((313*x)/200 - 1689/2000))/25 + (42471*cos((1573*x)/1000 + 1153/500))/80 + (937443*cos((1849*x)/2500 + 441/250))/62500;
Desired_Symbolic_Result = der(X)
Desired_Numeric_Result = vpa(der(X))
Desired_Symbolic_Result =
(937443*cos(26327/250))/62500 + (42471*cos(111263/500))/80 + (13459*cos(436511/2000))/25
Desired_Numeric_Result =
-503.67380291547475440432522297924
Beginning in R2012a, you can create symbolic functions. You then work with them as you would any other function.
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Gavin Seddon le 13 Nov 2017
Hello, this is really trivial however histogram(X) does not use my values. So how do I instruct Matlab to use my X and Y values? GS.
Star Strider le 13 Nov 2017
The documentation provides guidance:
histogram(X,edgvct)
or if you have two arrays and you want a 2-dimensional histogram, use the histogram2 function. You may have to provide a second vector of edges for the ‘Y’ data as well. See the documentation for details.

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