how to implement cartesian coordinates

2013 3 29
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I have a image
http://imgur.com/EOyLRe6
which consists of cartesian coordinates,plz tell how to implement these coordinates,which function must be used
Kindly help

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Walter Roberson
Walter Roberson 2013-3-29
What is the context for that? It does not appear to be general Cartesian coordinates: it appears to be the expression in Cartesian coordinates of something like a wave function or a rotation.
kash
kash 2013-3-29
it is equation taken from
http://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations
which is Navier–Stokes equations
kash
kash 2013-3-29
its for fluid flow

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回答（1 个）

Walter Roberson
Walter Roberson 2013-3-29

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Use the symbolic toolbox function diff()

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kash
kash 2013-3-29
walter tried example1 in
http://www.mathworks.in/help/symbolic/mupad_ref/diff.html
i got error as
Undefined function or variable 'x'.
when i gave x=2
i got
ans =
[]
y i get such answer
kash
kash 2013-3-29
i tried syms x and got answer
syms x
f=x^3
p=diff(f)
a=subs(f,[x],2)
i got answer
p =
3*x^2
a =
8
a must be 12,why i get 8
Walter Roberson
Walter Roberson 2013-3-29
8 is correct. f = x^3, and 2^3 is 8.
kash
kash 2013-4-3
after differentation we get 3x^2,so the answer should be 12 rite
Walter Roberson
Walter Roberson 2013-4-3
No, the answer for a=subs(f,[x],2) should be 8. Calculating diff(f) makes no difference to the value you find by substituting something into f.

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kash
kash
2013-3-29

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