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edited Mar 3, 2020 at 14:24

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I want to write a function that takes the derivative of f wrt y1 and then find the root of this derivative when y1 equals y2. The function f contains several integrals, y1, y2 and x also appear as limits of the integrals. Eventually I would like to be able to vary x and see how the root changes.

Below is the closest I've gotten, but doesn't work.

fd[x_?NumericQ, y1_?NumericQ, y2_?NumericQ] := D[f[x, y1, y2], y1]
fr[x_?NumericQ, y1_?NumericQ, y10_?NumericQ] := 
 y1 /. FindRoot[fd[x, y1, y1]y1]==0, {y1, y10}]

Am I missing a HoldAll condition for y2 in fd?

I want to write a function that takes the derivative of f wrt y1 and then find the root of this derivative when y1 equals y2. The function f contains several integrals, y1, y2 and x also appear as limits of the integrals. Eventually I would like to be able to vary x and see how the root changes.

Below is the closest I've gotten, but doesn't work.

fd[x_?NumericQ, y1_?NumericQ, y2_?NumericQ] := D[f[x, y1, y2], y1]
fr[x_?NumericQ, y1_?NumericQ, y10_?NumericQ] := 
 y1 /. FindRoot[fd[x, y1, y1], {y1, y10}]

Am I missing a HoldAll condition for y2 in fd?

I want to write a function that takes the derivative of f wrt y1 and then find the root of this derivative when y1 equals y2. The function f contains several integrals, y1, y2 and x also appear as limits of the integrals. Eventually I would like to be able to vary x and see how the root changes.

Below is the closest I've gotten, but doesn't work.

fd[x_?NumericQ, y1_?NumericQ, y2_?NumericQ] := D[f[x, y1, y2], y1]
fr[x_?NumericQ, y10_?NumericQ] := 
 y1 /. FindRoot[fd[x, y1, y1]==0, {y1, y10}]

Am I missing a HoldAll condition for y2 in fd?

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edited Mar 3, 2020 at 14:14

user2799609

51
5

I want to write a function that takes the derivative of f wrt y1 and then find the root of this derivative when y1 equals y2. The function f contains several integrals, y1, y2 and x also appear as limits of the integrals. Eventually I would like to be able to vary x and see how the root changes.

Below is the closest I've gotten, but doesn't work.

fd[x_?NumericQ, y1_?NumericQ, y2_?NumericQ] := D[f[x, y1, y2], y1]
fr[x_?NumericQ, y1_?NumericQ, y10_?NumericQ] := 
 y1 /. FindRoot[fd[x, y1, y1], {y1, y10}]

Am I missing a HoldAll condition for y2 in fd?

I want to write a function that takes the derivative of f wrt y1 and then find the root of this derivative when y1 equals y2.

Below is the closest I've gotten, but doesn't work.

fd[x_?NumericQ, y1_?NumericQ, y2_?NumericQ] := D[f[x, y1, y2], y1]
fr[x_?NumericQ, y1_?NumericQ, y10_?NumericQ] := 
 y1 /. FindRoot[fd[x, y1, y1], {y1, y10}]

Am I missing a HoldAll condition for y2 in fd?

I want to write a function that takes the derivative of f wrt y1 and then find the root of this derivative when y1 equals y2. The function f contains several integrals, y1, y2 and x also appear as limits of the integrals. Eventually I would like to be able to vary x and see how the root changes.

Below is the closest I've gotten, but doesn't work.

fd[x_?NumericQ, y1_?NumericQ, y2_?NumericQ] := D[f[x, y1, y2], y1]
fr[x_?NumericQ, y1_?NumericQ, y10_?NumericQ] := 
 y1 /. FindRoot[fd[x, y1, y1], {y1, y10}]

Am I missing a HoldAll condition for y2 in fd?

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asked Mar 3, 2020 at 14:03

user2799609

51
5

FindRoot of Derivative

I want to write a function that takes the derivative of f wrt y1 and then find the root of this derivative when y1 equals y2.

Below is the closest I've gotten, but doesn't work.

fd[x_?NumericQ, y1_?NumericQ, y2_?NumericQ] := D[f[x, y1, y2], y1]
fr[x_?NumericQ, y1_?NumericQ, y10_?NumericQ] := 
 y1 /. FindRoot[fd[x, y1, y1], {y1, y10}]

Am I missing a HoldAll condition for y2 in fd?

equation-solving calculus-and-analysis

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FindRoot of Derivative