### Author Topic: Notation & Linear  (Read 656 times)

#### Zhiya Lou

• Jr. Member
• Posts: 12
• Karma: 12
##### Notation & Linear
« on: September 16, 2018, 08:36:44 PM »
HI, I don't understand the notation from these question (sec1.3); And also about its linear/non-linear property... Thanks

22) $𝑢_{𝑥𝑥}+u_{𝑦𝑦}+𝑢𝑢_𝑥+𝑢𝑢_𝑦+u=0$

(why is it non linear?)

23)  $u_{𝑥𝑥𝑥𝑥}+2u_{𝑥𝑥𝑦𝑦}+𝑢_{𝑦𝑦𝑦𝑦}=0$

« Last Edit: September 16, 2018, 10:34:09 PM by Victor Ivrii »

#### Kathryn Bucci

• Jr. Member
• Posts: 6
• Karma: 2
##### Re: Notation & Linear
« Reply #1 on: September 16, 2018, 10:03:41 PM »
$u_x$ = partial derivative of $u$ with respect to $x$
$u_{xx}$ = second partial derivative of $u$ with respect to $x$

22) is not linear because of the two terms where u is multiplied by $u_x$ and $u_y$

I fixed math expressions for both of you. "Edit" to see how it should be done-V.I.
« Last Edit: September 16, 2018, 10:35:28 PM by Victor Ivrii »