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Re: Gradient of two dimensional field [message #8291 is a reply to message #8200]

Wed, 19 February 1997 00:00

stockwell
Messages: 1
Registered: February 1997

Junior Member

In article <yckohdg23jj.fsf@hmi.de> Wilpert_Martin <wilpert-m@hmi.de> writes:
> From: Wilpert_Martin <wilpert-m@hmi.de>
> Subject: Gradient of two dimensional field
> Date: 19 Feb 1997 16:56:00 +0100

> Hi everybody,
> we want to determine the electrical field from a given potential,
> i.e. we have to calculate the gradient of a two dimensional array.
> Has anybody a idl-pvwave procedure to do this task?
> Thank you in advance
> Martin Wilpert

The gradient is just (d/dx , d/dy)f(x,y)
so you can take the deriv() function on the rows and then the columns
"The DERIV function performs numerical differentiation using 3-point,
Lagrangian interpolation and returns the derivative."

so do this:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;
;; array holds your potential function of size (len,len)
dx = fltarr(len,len)
dy = fltarr(len,len)
; my apologies for the for loop
for i = 0,len-1 do dx(*,i) = deriv(array(0:len-1,i))
for i = 0,len-1 do dy(i,*) = deriv(phase(i,0:len-1))
endfor
vel,dx,dy
end
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;

dx holds the x component of the gradient
dy holds the y component of the gradient

cheers,
bob

============================================================ =========
R. G. Stockwell | Space and Atmospheric Research Group
Phone: 519-679-2111 X6411 | University of Western Ontario
Fax: 519-661-3129 | London, Ontario, Canada
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email: stockwell@uwo.ca
WWW: http://www.sar.physics.uwo.ca/~stockwell/time_series.html
" If I have not seen as far as other men, it's
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[Message index]

		Gradient of two dimensional field By: Wilpert_Martin on Wed, 19 February 1997 00:00
		Re: Gradient of two dimensional field By: Andy Loughe on Wed, 19 February 1997 00:00
		Re: Gradient of two dimensional field By: davidf on Wed, 19 February 1997 00:00
		Re: Gradient of two dimensional field By: stockwell on Wed, 19 February 1997 00:00
		Re: Gradient of two dimensional field By: Andy Loughe on Wed, 19 February 1997 00:00
		Re: Gradient of two dimensional field By: bowman on Wed, 19 February 1997 00:00
		Re: Gradient of two dimensional field By: brian.jackel on Wed, 19 February 1997 00:00
		Re: Gradient of two dimensional field By: Mirko Vukovic on Wed, 19 February 1997 00:00
		Re: Gradient of two dimensional field By: Andy Loughe on Mon, 03 March 1997 00:00

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