#2532 partial derivative is wrong

None
closed
nobody
None
5
2013-01-11
2013-01-11
No

irf(a1,a2,b,c,th1,th2) := c+(1-c)/(1+exp(-(a1th1+a2th2+b)));
diff(log(1-irf(a1,a2,b,c,th1,th2)),a1);

obtains:

-((1-c)th1%e^(-a2th2-a1th1-b))/((%e^(-a2th2-a1th1-b)+1)^2(-(1-c)/(%e^(-a2th2-a1*th1-b)+1)-c+1))

Compare output to Wolfram Alpha. For Wolfram Alpha, I had to rename some of the variables:

d/dx log(1- (c+(1-c)/(1+exp(-(xf+yg+z*h+b)))))

Obtains:

f/(e^(b+fx+gy+h*z)+1)-f

Discussion

  • Raymond Toy

    Raymond Toy - 2013-01-11

    I don't see anything wrong with maxima's result. It's not as simple as it could be, but it doesn't look wrong. Using ratsimp makes the expression simpler.

    Can you point out what the problem is?

     
  • Joshua Pritikin

    Joshua Pritikin - 2013-01-11

    Sorry, I guess both results are the same.

     
  • Raymond Toy

    Raymond Toy - 2013-01-11
    • status: open --> closed
     
  • Raymond Toy

    Raymond Toy - 2013-01-11

    No problem. Closing this bug.

     

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