partial derivative and quotient rule and a product rule

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ehsan Zahoor
ehsan Zahoor 2017-3-15
评论： Walter Roberson 2020-3-29
hi all i have a partial derivative which needs to be programmed on matlab.
struggling atm. help would be grateful.
m=(-10.4a-1.2b+1.2ab+28.8)(9.2ab-9.2ab^2)/(16b-16b^2+(7.1-2.3a)*(9.2a-9.2ab)+32.66ab-10.58ba^2)
we need to differentiate m with respect to a and b and equal it to zero.
we want to find out a and b when the above mentioned scenario is equal to zero.

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回答（1 个）

MICHAEL RILEY
MICHAEL RILEY 2020-3-28
编辑：MICHAEL RILEY 2020-3-28
Well the first issue you have, is that syntactically your code will not run. You are missing operators in your equation for matlab to run. I have expanded your equation, really more than I normally would, to show you the operators you are missing. Also for the ab^2 terms it is unclear if you are square both or not.
Secondly, you need to use the symbolic library to take the derivative with respect to a or b
syms a b
m = (-10.4 * a - 1.2 * b + 1.2 * a * b + 28.8) * (9.2 * a * b - 9.2 * a * b ^ 2) /...
(16 * b - 16 * b ^ 2 + (7.1 - 2.3 * a) * (9.2 * a - 9.2 * a * b) +...
32.66 * a * b - 10.58 * b * a ^ 2)
dm_da = diff(m, a)
dm_db = diff(m, b)
m =
m =
m =
  2 个评论
Khawla Albanna
Khawla Albanna 2020-3-28
Hi, I have a question how to download the symbolic library. Because I am getting an error with my codes while using syms.
Walter Roberson
Walter Roberson 2020-3-29
Khawla Albanna is it possible that you are using R2019a on MacOS Catalina ? (I cannot remember if it applies to R2019b as well) ? If so then you should upgrade to at least R2019b Update 4.

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