Sumatory in LaTeX

1. Dec 5, 2011

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!

2. Dec 5, 2011

D H

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

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

3. Dec 5, 2011

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
$$\frac{\partial}{\partial x}$$

PFmet

4. Dec 5, 2011

D H

Staff Emeritus
\mathcal L(U) = f(x)

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

5. Dec 5, 2011

PFmet

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

PFmet

6. Dec 5, 2011

Staff: Mentor

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

7. Dec 5, 2011

PFmet

Thanks Mark! My language is Spanish! :)