Symbolic Integration

Hi everybody,

I have a little question about 'int' function. I have this code:

>> syms x y  
>> int(x+y,x)

so I want to know why is this the result?:

ans =   
(x + y)^2/2

instead of:

x^2/2+x*y

I'm a little confused about it, I hope you can help me understand.

Answer 1

[Teja Muppirala]

Both answers are correct.

d/dx[ (x+y)^2/2 ] = d/dx[ x^2/2 + x*y + y^2/2 ] = x + y

d/dx[ x^2/2 + x*y ] = x + y

The ambiguity lies in the constant of integration. In the first case the constant of integration ends up being y^2/2.

If you really want to enforce that the constant of integration is zero then do:

F = int(x+y,x,0,x)
expand(F)

[Jonathan]

Thank you, now I understand how the function works.

Answer 2

[Walter Roberson]

Odd, I don't get that in Maple; unfortunately I don't have the Symbolic Toolbox to test with.