# How to find the inverse of a function numerically

151 views (last 30 days)
BeeTiaw on 28 Jan 2019
Commented: BeeTiaw on 28 Jan 2019
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 on 28 Jan 2019
But you wrote you already used "roots" on the example:
p = [m3 m2 m1 -z 1.0];
zeta = roots(p)
BeeTiaw on 28 Jan 2019
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 on 28 Jan 2019
Oh probably I can do it by multiplying them with

John D'Errico on 28 Jan 2019
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 on 28 Jan 2019
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 on 28 Jan 2019
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