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(50g) Inverse Function
02-05-2020, 08:43 AM
Post: #1
(50g) Inverse Function
Hello 50g fans
In the official HP forum (calculators) arised the question: it is possible to plot the inverse of a function and the example was: f(x) = x^3 + x^2 +1?

The answer is yes. Generally you can define two functions:

'FOO' (This code is produced by the command 'DEF'):


<< -> X 'X^3 + X^2 +1' >>  @@ that is the original function mentioned above

and 'IFOO':

<< -> X 
      << 'FOO(AG) - X = 0.'  @@ equation for command 'ROOT'
          'AG'                      @@ variable for solving
          0.                        @@ starting value
          ROOT                   @@ solving command

Only caution the variable 'AG' is handled as a global variable, which appears in your working directory and should be deleted after usage of 'IFOO'.

It is good working in approximation mode. And the plotting area should be limited to areas with same montonic characteristics. Sometimes you get artefacts in plotting, you should be aware of this possibility.
In the pic you see such a artefact in the third sector of the coordinate system (the straight line vertical to the x-axis). The original function is also displayed.

Define in the 'y=" form 'Y1(x) = IFOO(X)' and set the values for x- and y-coordinates in the form 'WIN' and you get your inverse function plotted.

Certainley you can use 'IFOO' although only for seeking a special root. And you can extend 'IFOO' by a second variable for the starting value.

Have fun and I'm pleased about comments and critics.
Sincerely peacecalc

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Messages In This Thread
(50g) Inverse Function - peacecalc - 02-05-2020 08:43 AM
RE: (50g) Inverse Function - Albert Chan - 02-05-2020, 11:03 AM
RE: (50g) Inverse Function - Joe Horn - 02-05-2020, 01:09 PM
RE: (50g) Inverse Function - peacecalc - 02-05-2020, 03:17 PM
RE: (50g) Inverse Function - peacecalc - 02-05-2020, 06:47 PM

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