How to convert a char letter into a double which is still a letter.

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Alfonso Rodriguez on 10 Jul 2020
Commented: Alfonso Rodriguez on 15 Jul 2020 at 0:37
How do i convert this variable:
graph which is a char with value = t
into a variable that remains with the same value = t, but it is read by Matlab as a double.
I´ve been trying to use str2double but it returns a NAN. If I use str2num it returns an empty vector.
I need to use the t value as a double in order to graph with the area() function.

1 Comment

Alfonso Rodriguez on 13 Jul 2020 at 23:46
Thanks Walter, Image analyst and Stephen. I am trying to make a GUI that graphs the area under the curve of a syms f(x) (user) function. The area function only works for numerical integration so I can´t use it with a symbolic integration.

Walter Roberson on 10 Jul 2020
If you are getting user inputs that are formula, then you should use str2func() to turn them into function handles.
Alternately, if you have the symbolic toolbox, you can use str2sym() to turn them into symbolic expressions.

Show 1 older comment
Alfonso Rodriguez on 14 Jul 2020 at 13:21
I wanted to get the user "string" func = get(edit, string) and then convert it to a numerical function that has x and y values in order to graph the area under the curve with the area() function.
Walter Roberson on 14 Jul 2020 at 19:32
S = get(handles.edit1, 'string');
v = symvar(S);
func = str2func( sprintf('@(%s) %s', v{1}, S) );
Alfonso Rodriguez on 15 Jul 2020 at 0:37
Thanks Again Walter. I didn´t knew symvar() existed.

Image Analyst on 10 Jul 2020
What value do you want t to have when being considered as a number? It's ASCII value? It's position in the alphabet (20)? Perhaps this helps:
ch = 't'
n = ch - 'a' + 1
ch =
't'
n =
20
Or do you simply want a variable named "t" that has a value you want, like 10, such that you could do this:
t = 10 % t now has the value 10
t2 = t * 2 % Multiply t by 2 to get 20
t =
10
t2 =
20
I have no idea what you mean when you say " t value as a double in order to graph with the area() function". Is t an N-by-2 list of (x,y) coordinates?
Please explain what you mean in more words, and with a desired output diagram/graph, but only after you read this link.

Alfonso Rodriguez on 13 Jul 2020 at 23:49
Thanks Image analyst. I am trying to make a GUI that graphs the area under the curve of a syms f(x) (user) function. The area function only works for numerical integration so I can´t use it with a symbolic integration.
I wanted to get the user "string" func = get(edit, string) and then convert it to a numerical function that has x and y values in order to graph the area under the curve with the area() function.
Image Analyst on 14 Jul 2020 at 3:10
Seems like you should have accepted Walter's answer rather than mine.