Plot of an curve and its equation

Hello;

I'm trying to get an equation of the plot and before trying to get this I got this plot to see if I can catch it truly and it does.

And here what I ve done till now;

x = 0 : 0.1 : 0.9;

y = [0.584459303
0.496427561
0.351841147
0.269416786
-0.080568348
0.354476019
0.155290021
0.755090485
0.612397011
0.505868478];

a=polyfit(x,y,9);
b=polyval(a,x);
plot(x,y,'ro',x,b)

And What I would like to have is the equation of this plot but once I tried to write the equation with the values from polyfit output I got a plot something completely different. May someone please help me? Thank you so much in advance..

x = 0 : 0.1 : 0.9;

y = [0.584459303
0.496427561
0.351841147
0.269416786
-0.080568348
0.354476019
0.155290021
0.755090485
0.612397011
0.505868478];

c= [214387.3975	-859079.8412 1444444.664	-1323346.187 717335.5313	-233431.4118	44018.3122	-4332.146236 165.7218241	0.584459303];


vel = c.*x';

plot(x,vel,'b','LineWidth',2)

Answer 1

[VBBV]

x = 0 : 0.1 : 0.9;

y = [0.584459303
0.496427561
0.351841147
0.269416786
-0.080568348
0.354476019
0.155290021
0.755090485
0.612397011
0.505868478];

a=polyfit(x,y,9)

a = 1×10

1.0e+06 * 0.2144 -0.8591 1.4444 -1.3233 0.7173 -0.2334 0.0440 -0.0043 0.0002 0.0000

b=polyval(a,x)

b = 1×10

0.5845 0.4964 0.3518 0.2694 -0.0806 0.3545 0.1553 0.7551 0.6124 0.5059

plot(x,y,'ro',x,b)

x = 0 : 0.1 : 0.9;

y = [0.584459303
0.496427561
0.351841147
0.269416786
-0.080568348
0.354476019
0.155290021
0.755090485
0.612397011
0.505868478];

c= [214387.3975	-859079.8412 1444444.664	-1323346.187 717335.5313	-233431.4118	44018.3122	-4332.146236 165.7218241	0.584459303];

vel = max(b.*x')

vel = 1×10

0.5260 0.4468 0.3167 0.2425 0 0.3190 0.1398 0.6796 0.5512 0.4553

plot(x,vel,'b-','LineWidth',2)

[VBBV]

use pol2sym to get equation for the plot

[OLuxanna]

thank you so much Sir for your help. It means a lot.