Ndtyhij

For the purpose of deforming a 3D mesh, I am looking for a formula to generate a curve I could evaluate like the following:

Its shape would be more or less a simplified version of wind waves over an ocean, where it starts slowly and ends more abruptly.

Which formula, if any, could allow me to draw such curve ?

Try the function

$$f(x)=arctanleft(frac{asin(x-c)}{b+acos x}right) + d$$

Also try $f(f(x))$ and other compositions of $f$ with itself.

The image shows the function $f(f(x))$, with $a=0.9$, $b=1$, $c=0.7$, $d=0.4$.

I recommend that you use desmos to preview the function. For your convenience, here is a template that I have created. Just change the sliders to adjust the constants to your liking. You can also scale the $x$-axis if the peaks are spread out too much.

I hope this helps.

@Haris Gusic : I have seen your solution which fits nicely the objectives of the asker with its 3 different tunable parameters.

I propose here two alternatives, one which is more intuitive, using linear algebra, the other one which is more 'numerical analysis' oriented.

1) I have been striken by the fact that the curve desired by Aybe is a perspective (or shadow) of a sine curve (or a power of a sine curve). Let us see it on the (red) curve of $y=sin(x)^n$ and its (blue) perspective image, which is an alternate answer to the question, with parametric equations given by

$$begin{cases}x&=&t+0.8sin(t)^n\y&=&0.1sin(t)^nend{cases} text{here, with } n=4.$$

Why that ? This "shadowing effect" is rendered by a so-called "skewing" or "transvection" linear operation with an upper triangular matrix:

$$color{blue}{binom{x}{y}}=begin{pmatrix}1&0.8\0&0.1end{pmatrix}color{red}{binom{t}{sin(t)^n}}$$

(this matrix reflects the fact that the horizontal direction is preserved whereas the former vertical direction has been bent rightwards).

Remark : the second column entries of the matrix as well as the sine exponent are tunable... You can even, in this way, obtain breaking waves...

Fig. 1. A linear algebra solution : the blue curve as a "shadow" of the red curve.

2) A "numerical analysis" method using quadratic splines.

I will not enter into the details because it is not sure at all that you are acquainted with such curves, which are made of parabolas connected in a "smooth" way.

Here is the Matlab program that explains all (notice the red, magenta and plus parabola with right translation variable $k$) and the figure it generates :

clear all;close all;hold on;

t=0:0.01:1;

for k=0:5:15

    plot(2*t+k,t.^2,'r');

    plot(-2*t.^2+4*t+2+k,-4*t.^2+4*t+1,'m');

    plot(4+t.^2+k,(1-t).^2,'b');

end;

Fig. 2 : A quadratic spline solution based on 3 parabolas (red, magenta, blue) connected in a smooth way, repeated "ad libidum".