partial derivative and quotient rule and a product rule

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.

[Torsten]

help diff
help solve

Best wishes

Torsten.

Answer 1

[MICHAEL RILEY]

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 =

[Khawla Albanna]

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]

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.