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Topic: How to calculate the partial derivative?
Replies: 4   Last Post: Nov 23, 2012 3:35 AM

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Bob Hanlon

Posts: 906
Registered: 10/29/11
Re: How to calculate the partial derivative?
Posted: Nov 22, 2012 4:40 AM
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repl = {L1 -> a1 + b1*x + c1*y,
L2 -> a2 + b2*x + c2*y,
L3 -> a3 + b3*x + c3*y};

SetOptions[D, NonConstants -> {L1, L2, L3}];

NN = L1*L2;

DNex = D[NN, x] /. D[repl, x]

b2 L1 + b1 L2

DNex /. repl

b2 (a1 + b1 x + c1 y) + b1 (a2 + b2 x + c2 y)


Bob Hanlon


On Wed, Nov 21, 2012 at 7:48 PM, Tang Laoya <tanglaoya1989@gmail.com> wrote:
> Dear all,
>
> I am trying to calculate the partial derivative by mathematica, I have the following commands:
> L1=a1+b1*x+c1*y;
> L2=a2+b2*x+c2*y;
> L3=a3+b3*x+c3*y;
>
> NN=L1*L2;
>
> DNx=D[NN,x];
>
> I got the following result:
> DNex=b2 (a1+b1 x+c1 y)+b1 (a2+b2 x+c2 y)
>
> How to do to have the following result?
>
> DNex=b2*L1 + b1 * L2
>
>
> Thanks,
> Tang Laoya
>





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