Hello Radovan, you will read these few samples
They all fit univariate wrt to 'x'
The bivariate [xy, z] is as simple as univariate.
For this case, I'm only aware of ordinary polynomials. It does not
exclude orthogonal polynomials.
The complete Treasury suggests an Electronic Book [Mathsoft style]

1. Chemist is not fittable in Mathcad, Smath as well, only by hand.
2. Lorentz Peak is 10 parameters.
3. Laser 10 parameters [lasted ~ 1 month Mathsoft Collaboratory].

Jean

Genfit Chemist.sm (28 KiB) downloaded 75 time(s).
Genfit Oxyhemoglobin Reconciliation.sm (63 KiB) downloaded 65 time(s).
Genfit Lorentz Peak Fit...Laser.sm (57 KiB) downloaded 60 time(s).
Genfit Kirby_2 [Reduced].sm (74 KiB) downloaded 58 time(s).
Genfit Difficult Pharmacokinetics.sm (39 KiB) downloaded 65 time(s).
Genfit Pharmacokinetics.sm (42 KiB) downloaded 59 time(s).
Bivariate algo.sm (47 KiB) downloaded 65 time(s).