8 replies to this topic

[MasterJoda800]

I found a problem in the mod() function.
If i use it with numbers it works fine
(e.g. mod(5,2)=1)
but if i try to use it with variables it behaves very strange
e.g.
mod(x,y) gives x as result

although x and y are both undefined (they have no value)

I found this when trying to use mod in a while construction in my program that calculates a mod function. It gives very strange results.

Does anyone know whats wrong with it?

thanks

[TacoFred]

well, since x and y are not defined, the calc's modulus function has no way of calculating a remainder value, and cannot print out anything else
it would make more sense to output an error in my opinion......

[Daruosh]

Same here, Is it a BUG??

[SoftCalc]

mod(x,y) gives x as result
Does anyone know whats wrong with it?

<{POST_SNAPBACK}>

It is doing a polynomial "mod". Try mod(x^2+4*x+3,x^2+3*x+2) and you'll see what I mean

[SoftCalc]

Well it is a bug, and it isn't.... "mod" will give a result with variables because it is doing a polynomial "mod". For the following case where you've entered to polynomials it is a very nice feature...mod(x^2+4*x+3,x^2+3*x+2) x+1
If, on the other hand, you want to use a variable as a placeholder, it is a very bad feature....mod(x,5) 5
What it is doing in the graph/table is correct, but not expected. It is doing a polynomial "mod" when what you want is a numeric "mod" where "x" is a placeholder.

The graph and table application pre-evaluates the expression to speed things up. As an example, a complicated integral will graph much faster if it is pre-evaluated and reduced before graphing. In this case though, it is "pre-evaluating" "mod(x,5)" and getting "x".

NOTE: The same problem exists with the "gcd" function.

[Lianna]

I think the function you [MasterJoda] were looking for is:
Define moda(x,y)=simplify(x-y*int(x/y))
Define modap(x,y)=simplify(x-y*intg(x/y))
seq(moda(x,3),x,-5,5,1)
seq(modap(x,3),x,-5,5,1)
Difference is in negative x values.
Best regards,
Lianna