How to find the inverse of a function numerically

Hi expert,

Can someone tell me how is it possible to find the inverse of this function

in which z is a complex number and cannot be zero. , a and b are constant.

How to solve this function for ?

Data (Example)

The following is obtained using the following input:

for

theta=[
    0
    0.6981
    1.3963
    2.0944
    2.7925
    3.4907
    4.1888
    4.8869
    5.5851
    6.2832];

The results is:

z = [
   2.9400 + 0.0000i
   3.2277 + 2.1618i
   2.2730 + 1.2986i
   0.4557 - 2.2605i
  -1.4094 - 6.6606i
  -2.3950 - 9.7020i
  -1.9857 -10.1025i
  -0.4083 - 7.8642i
   1.5321 - 3.9596i
   2.9400 - 0.0000i   
];

Example:

I used Matlab function "roots" to solve the following inversion problem

by rearrange the function into:

and use to function "roots" to find the solution.

[Torsten]

For your example, there will be 4 zeta-values that satisfy the last equation. Which of them would you like to choose ?

[BeeTiaw]

This is a good question, @Torsten! Yes, it is true that there will be more than one solution. I normally choose the last solution.

But for now, how do we find those 4 values?

[Torsten]

"roots" is the correct function to use.

[BeeTiaw]

How to arrange the matrix for such function, Torsten?

I have provided an example. It is easy to do so if the function can be converted in a polynomial, but in my case, the function seems to be complicated. I really don't know how to form the matrix so that I can use "roots".

Can you help me please.

[Torsten]

Which matrix ?

[BeeTiaw]

To use "roots" we need a matrix as the input, aren't we?

For the above example, what would be the input?

Sorry, I am really clueless about this problem.

[Torsten]

But you wrote you already used "roots" on the example:

p = [m3 m2 m1 -z 1.0];
zeta = roots(p)

[BeeTiaw]

Torsten, the original question does not allow me to make such matrix.

How do I suppose to transform the following matrix into polynomial so that I can use "roots"?

Or, am I missing your point here?

[BeeTiaw]

Oh probably I can do it by multiplying them with

Answer 1

[John D'Errico]

Multiply by zeta^2, and collect terms. As long as zeta is not zero, that is not a problem. Your equation reduces to

b*m2 + (a + b*m1)*zeta - z*zeta^2 + (a*m1 + b)*zeta^3 + (a*m2)*zeta^4 == 0

We only need to worry about zeta==0 if either of b or m2 was zero. In that case, zeta==0 would be one of the roots of the above equation.

Of the coefficients of the above equation, all are apparently known, and have fixed values. So there are 4 roots.

Then the "inverse" is given as any of the 4 roots of that equation, thus:

zetaroots = solve(b*m2 + (a + b*m1)*zeta  - z*zeta^2 + (a*m1 + b)*zeta^3 + (a*m2)*zeta^4,zeta,'maxdegree',4);

You don't want me to write the entire expression in here, as it is a massive mess of terms.

The problem is, the "inverse" is a rather nasty mess of a function of z. There are 4 solutions. Even if I show only 5 digit numbers in that expression for all coefficients, it is still a nasty mess.

vpa(expand(subs(zetaroots,{a,b,m1,m2},[-2.0800,4.0800,0.5,-0.03])),5)
ans =
 - (0.16667*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2))/(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/6) - (0.16667*(10680.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 70.15*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 256.82*z^2*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) + 2868.6*z*(5.1962*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 6767.6*z - 8231.4*z^3 - 125699.0)^(1/2) + 106211.0*(5.1962*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 6767.6*z - 8231.4*z^3 - 125699.0)^(1/2) + 192.31*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2))^(1/2))/((0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/6)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/4)) - 12.179
   (0.16667*(10680.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 70.15*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 256.82*z^2*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) + 2868.6*z*(5.1962*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 6767.6*z - 8231.4*z^3 - 125699.0)^(1/2) + 106211.0*(5.1962*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 6767.6*z - 8231.4*z^3 - 125699.0)^(1/2) + 192.31*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2))^(1/2))/((0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/6)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/4)) - (0.16667*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2))/(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/6) - 12.179
   (0.16667*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2))/(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/6) - (0.16667*(10680.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 70.15*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 256.82*z^2*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 2868.6*z*(5.1962*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 6767.6*z - 8231.4*z^3 - 125699.0)^(1/2) - 106211.0*(5.1962*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 6767.6*z - 8231.4*z^3 - 125699.0)^(1/2) + 192.31*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2))^(1/2))/((0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/6)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/4)) - 12.179
   (0.16667*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2))/(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/6) + (0.16667*(10680.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 70.15*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 256.82*z^2*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2) - 2868.6*z*(5.1962*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 6767.6*z - 8231.4*z^3 - 125699.0)^(1/2) - 106211.0*(5.1962*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 6767.6*z - 8231.4*z^3 - 125699.0)^(1/2) + 192.31*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/2))^(1/2))/((0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/6)*(96.154*z*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 5340.2*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(1/3) + 9.0*(0.096225*(2.07e6*z^4 + 7.6638e7*z^3 + 1.1346e6*z^2 + 6.3008e7*z + 5.8506e8)^(1/2) - 125.33*z - 152.43*z^3 - 2327.6)^(2/3) + 256.82*z^2 + 70.15)^(1/4)) - 12.179

I'm not at all sure what you expected the inverse of your function would look like. But it is not pretty.

[BeeTiaw]

Hi, thanks!

I have posted another question related to this post which consider a much more generalised form of function. How do we determine the solution?

[BeeTiaw]

An answer for a much more generalised form of function is available here https://uk.mathworks.com/matlabcentral/answers/441867-tthe-inverse-of-a-function-numerically-with-n-terms