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plot tangentail vector [message #58032]

Sat, 12 January 2008 21:41

nakisa
Messages: 24
Registered: June 2007

Junior Member

hi everybody
I need plot on each (x,y) a tangentail vector with known magnitude , I
have a file with three columns , x ,y , A.
where A is the magnitude of vector .
can anybody help me ?
best,nakisa

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Re: plot tangentail vector [message #58078 is a reply to message #58032]

Wed, 16 January 2008 05:44

JMB
Messages: 13
Registered: January 2008

Junior Member

Does this short example help you?

N = 200
X = FINDGEN(N)
Y = 10*SIN(x/16)-10*COS(x/8+2)
A = abs(16*SIN(x[1:N-2]/4.))

PLOT, X, Y

vx=X[2:N-1]-X[1:N-2]
vy=(Y[2:N-1]-Y[0:N-3])/2.

Norm=A/sqrt(vx^2+vy^2)

ARROW,X[1:N-2],Y[1:N-2],X[1:N-2]+Norm*vx,Y[1:N-2]+Norm*vy,/
DATA,color=220
PLOT, X, Y, /noerase

END

Regards,

Jérôme

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Re: plot tangentail vector [message #58080 is a reply to message #58032]

Wed, 16 January 2008 05:19

Spon
Messages: 178
Registered: September 2007

Senior Member

On Jan 16, 4:47 am, nakisa <nakisa.noor...@gmail.com> wrote:
> Hi
> Arrow ,as far as I understand , give initial and final point and draw
> a vector. My case is different. I have the initial point and want to
> draw a tangential vector !so I can't use Arrow for this aim.
> Nakisa

In that case, maybe VELOVECT will do what you want? Although, surely
if you have the vectors' magnitudes and directions you can just use
ARROW after working out your X1/Y1 values? It may even be simpler than
trying to get your head around constructing the correct U & V arrays
for VELOVECT! :-)

Good luck!

Chris

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Re: plot tangentail vector [message #58192 is a reply to message #58078]

Fri, 18 January 2008 21:58

nakisa
Messages: 24
Registered: June 2007

Junior Member

hi Jerome
thanks but it isn't what I need. i want at each position (x,y) it
suppose a circle and plot a tangential vector with given magnitude !!!
nakisa

On Jan 16, 4:44 pm, JMB <jmb.lo...@gmail.com> wrote:
> Does this short example help you?
>
> N = 200
> X = FINDGEN(N)
> Y = 10*SIN(x/16)-10*COS(x/8+2)
> A = abs(16*SIN(x[1:N-2]/4.))
>
> PLOT, X, Y
>
> vx=X[2:N-1]-X[1:N-2]
> vy=(Y[2:N-1]-Y[0:N-3])/2.
>
> Norm=A/sqrt(vx^2+vy^2)
>
> ARROW,X[1:N-2],Y[1:N-2],X[1:N-2]+Norm*vx,Y[1:N-2]+Norm*vy,/
> DATA,color=220
> PLOT, X, Y, /noerase
>
> END
>
> Regards,
>
> Jérôme

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