Including Lines in Summation - Is it Possible?

[PFmet]

Hy everyone!

I want to include this two lines:
m,n
m+n=k
but only in the bottom of the sumatory. Is that possible?

Thanks in advance for the help!

 

[D H]

\sum_{\substack{m,n\\m+n=k}}

$$\sum_{\substack{m,n\\m+n=k}}$$

 

[PFmet]

Awesome! Thank U very much!

Can I ask U something else? Do you know if I can include text in cursive? The sentence is

$$\textbf{L} (U) = f(x)$$

where L (that should be in cursive) is a differential operator like
$$\frac{\partial}{\partial x}$$

Thanks in advance again!

PFmet

 

[D H]

\mathcal L(U) = f(x)

$$\mathcal L(U) = f(x)$$

 

[PFmet]

Wow DH! Thank U very very much! My work is perfect now.

GRACIAS! DANKE! OBRIGADA! = THANKS!

PFmet

 

[Mark44]

I want to include this two lines:
m,n
m+n=k
but only in the bottom of the sumatory. Is that possible?

We call this symbol - $\sum$ -- a summation, in English.

 

[PFmet]

We call this symbol - $\sum$ -- a summation, in English.

Thanks Mark! My language is Spanish! :)