Symbolic entry of rem function

When entering the following symbolic code using the remainder (rem) function, Matlab returns x(t,P) = 0, which is clearly wrong.

syms t P

x(t, P) = rem(t,P);

x

I have tried all combinations of sym, syms, symfun, but the result is the same. I need to enter the symbolic function x = rem(t,P) to perform symbolic integration on it over the period t = [0:P].

Help is appreciated, thanks

Answer 1

[Star Strider]

Wrong function. Use mod instead for symbolic operations:

syms t P

x(t, P) = mod(t,P);

x

returns:

x(t, P) =

t*(1 mod P)

[Nate]

There is one problem: when t = P or t > P, it breaks down:

syms t P

x(t, P) = mod(t, P);

x(0,2) returns 0 (correct)

x(1,2) returns 1 (correct)

x(2,2) returns 2 (incorrect)

x(3,2) returns 3 (incorrect)

Correct values:

rem(2,2) or mod(2,2) should equal 0

rem(3,2) or mod(3,2) should equal 1

Any other suggestions?

[Star Strider]

It works if you just use the mod function directly:

syms t P
m1 =mod(0,2)
m2 =mod(1,2)
m3 =mod(2,2)
m4 =mod(3,2)

produces:

m1 =

       0

m2 =

       1

m3 =

       0

m4 =

       1

EDIT — Added:

It also works if you define your own function for mod:

syms t P

x = symfun(t-floor(t/P)*P, [t P]);

m1 =x(0,2)
m2 =x(1,2)
m3 =x(2,2)
m4 =x(3,2)

The result is as m1...m4 using the built-in mod function, so I won’t repeat them.

[Nate]

Brilliant, thanks so much.

[Star Strider]

My pleasure!

It was a fun challenge for me!

[DmArcher]

When I type your code I get some errors. Is it possible that you can tell me where I did it wrong? Thx.