Finding parameters to y = x/ A*x + B equation

**nenadpmf** · 09-03-2011, 01:49 PM

Hi!
I wanted to know how to fit my data to function y=x / A*x + B, and i also need to know parameters A and B. If it's of any help to you, here is my data set:

x y
10 0.2
20 0.276
30 0.304
40 0.316
50 0.323
60 0.327
70 0.328
80 0.329
900 0.330

Parameter A must be something around 0.33 - 0.35 but for B I haven't got a clue . . .

Thank You

**zbor** · 09-03-2011, 01:57 PM

Is this x/(A*x) ? that's same as 1/A (for x <> 0) so, no x variable...

**nenadpmf** · 09-03-2011, 03:47 PM

x
--------------------- = y , i hope you'll get the idea of me writing fractions like that . . .
x*A + B

I wasn't very careful while writing, but this is what equation should look like . . . And parameter A should give value of y for infinite x . . . thats some chemical kinetics stuff, maximal adsorption over infinite time . . .

**shg** · 09-03-2011, 05:37 PM

One way:

       ---B--- --C--- --D-- -------------------E-------------------
   2         A  2.822                                              
   3         B 17.357                                              
   4   RMS Err 0.0113       C4: {=SQRT(AVERAGE((D7:D15-C7:C15)^2))}
   5                                                               
   6      x      y    F(x)                                         
   7        10  0.200 0.219 D7 and down: =x/(A*x + B)              
   8        20  0.276 0.271                                        
   9        30  0.304 0.294                                        
  10        40  0.316 0.307                                        
  11        50  0.323 0.315                                        
  12        60  0.327 0.321                                        
  13        70  0.328 0.326                                        
  14        80  0.329 0.329                                        
  15       900  0.330 0.352

I set A and B initially to 1, and then used Solver to minimize C4 by changing A and B.

**nenadpmf** · 09-03-2011, 06:54 PM

Hey, thnx! This actually works quite well! But is there any way to assign it to macro? I've tried doing the procedure while recording the macro, but when I run it, it wont work . . .