Substituting and evaluating function

3 vues (au cours des 30 derniers jours)
Gavin Seddon
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>tomupad (line 1243)
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
  2 commentaires
Stephen23 le 13 Sep 2017
What is der? Is it symbolic, or is it a simple function handle?
Gavin Seddon
Gavin Seddon le 13 Sep 2017
Hello, der is the symbolic function that is the result of dIff fx.

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Star Strider
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 =
Beginning in R2012a, you can create symbolic functions. You then work with them as you would any other function.
  24 commentaires
Gavin Seddon
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
Star Strider le 13 Nov 2017
The documentation provides guidance:
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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