Question about CAS and Graphing

[Nigel (UK)]

(09-20-2014 08:59 PM)Mysilmaril Wrote:  Let's say you perform the following integration in CAS, int(x,x). The result is 1/2 * x^2. Now, let's say you want to plot the result as a function, f(X) using the Function app.

If I switch to the Function app, I can push the "Menu" button to get the result of my integration in CAS. However, I can't enter this equation because it uses a lower case 'x' instead of an upper case 'X'.

To plot the equation you have to swap out the 'x' with a 'X'. This isn't very efficient for larger equations. What's the point of getting an equation from CAS if you can't use it?

One way around the problem that hasn't been mentioned yet is the following.

Suppose you have a potentially complicated function of x (or any other variable) on the CAS screen - call it f(x).

Copy f(x) to the command line in CAS and use the "|" template with x='X' as the substitution. This replaces x with X; you can then copy the new expression from CAS into the graphing app with the "Menu" button as you describe above.

There are a couple of points to note.

First, the single quote marks around X are needed - without them x is replaced with the numerical value of X (and because X is a Home variable, it always has a numerical value; it is never undefined).

Second, you can't use "Ans" instead of copying f(x) directly into the command line. I think that the substitution command carries out the substitution before evaluating its first argument, which is normally what you want. This fails when the first argument is Ans. The substitution is carried out on 'Ans', leaving it unchanged, and then Ans is evaluated giving the original expression back again. Ans needs to be treated with care!

Nigel (UK)