diff() function

11092014, 02:29 PM
Post: #1




diff() function
A diff() problem:
Example: f(x,y):+x²2*x*y+3*y²+2*x2*y 1.) diff(f(x,y),x) > 2.*x2.*y+2. 2.) diff(f(x,y),y) > 2*x+6*y2 x  direction: 3.) diff(diff(f(x,y),x)) > 2 4.) diff( 2.*x2.*y+2,x) > 2 5.) diff(f(x,y),x$2) > 2 y  direction: 6.) diff(diff(f(x,y),y)) > 2 7.) diff(2*x+6*y2,y) > 6 8.) diff(f(x,y),y$2) > 6 The second derivative in the xdirection worked properly. The second derivative in the ydirection worked improperly in the red highlighted case(??) (The template key entry method worked properly for these examples.) 

11092014, 02:51 PM
Post: #2




RE: diff() function
Since you didn't put in a second variable of differentiation, it defaults to 'x'. So 2 is the correct answer as it is the mixed partial derivative.
Graph 3D  QPI  SolveSys 

11092014, 05:53 PM
Post: #3




RE: diff() function
(11092014 02:29 PM)DrD Wrote: 6.) diff(diff(f(x,y),y)) > 2 Modifying step (6.) thus: diff(f(x,y),y,y) works. In step (8.) (given by the y$2), y is sufficiently specified as the variable to use for each following derivative? [or]
In the case: ∂(diff(f(x,hpdiffx),hpdiffx),y) > 6 The variable of differentiation is specified only once. That's a lot to remember. The user guide description for the diff() topic could be expanded for more clarity. I think that about wraps up my interest in this function. Thanks Han, for taking all the time explaining details! Dale 

« Next Oldest  Next Newest »

User(s) browsing this thread: 1 Guest(s)