Hi @Marcel,
To force all input variables to appear in the solutions, you can use the "Force solutions to include all variables?" option available in the Advanced tab. It works for custom searches, so if your custom formula is
y = f(x, y)/f(x, y, z)
then the first term will contain both x and y, and the second one will contain x, y, and z.
Further, is there a maximum number of variables I can use in custom search?
No, you can use as many variables as you like, but the search will become slower as the number of variables increases. Also, if you want to use all variables except a few, it may be easier to write
y = f(~x, ~y)
which means "use all variables as input except for x and y".
Last question, is it possible to define a constant in the custom search which appears at different places in the formula (so in fact two f()'s which must be equal to each other)?
Not yet, but v2.23, which should be released in the coming days, will have this feature.
