Using FROOT recursively on the HP-71?

[Valentin Albillo]

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Hi again, Àngel:

(02-04-2017 01:16 PM)Ángel Martin Wrote:  I assumed FNROOT will return just *one* value (the first root found within the interval), but what does FVAR mean in the statement below:

DEF FNF = X*X+Y*Y <or whatever your function is>
DEF FNY (X) = FNROOT (Y1, Y2, FNF (X, FVAR ) )

Did you read the PDF article of mine I mentioned ? The first line of code you include above does not appear in any of the two examples in my article and in fact it's wrong, you'd need two user-defined functions, FNF(X,Y) and FNG(X,y) (not just a parameterless one), like this:

10 DEF FNF(X,Y)=f(x,y)
20 DEF FNG(X,Y)=g(x,y)

your single FNF above isn't sufficient and further, it lacks the X,Y parameters. Also, as seen in both my examples, you need a second FNROOT which calls the nested FNROOT in your second line above which is taken from my second example.

FVAR is to FNROOT as IVAR is to INTEGRAL, i.e., the variable you're solving for (integrating). In other words, it stands for the unknown being solved for (the "x" in "x^2-2=0", so to say).

I'd suggest you key-in any or both of my examples, run them to see how they work, and if needed do include some PRINT or DISP debugging statements to see how the variables are converging on the final X,Y solutions. This will probably help a lot.

Best regards.
V.