How to plot on the same graph with for cycles with Gnuplot?

Question

I want to fit multiple data set and plot the result on the same graph, what I' am doing is:

do for [i=2:500]{
fit f(x) "myData" using 1:i via a,b
plot f(x)
}

The fit works fine, the big problem is that this code produce a different plot at each iteration. I would like to have all the fitted functions in a single graph. Is there any way ?

Answer 1

I guess you cannot fit and plot in the same loop. Well, there would be the multiplot environment (check help multiplot), but I guess this is not your idea. So, you can fit in a do for loop and store the fitted parameters in an array for later use during plotting. You didn't specify any function, so I assumed something. Check the following minimized example:

Code:

### fitting in a loop
reset session

$Data <<EOD
1   1   6    4
2   4  10    1  
3   9  15    0
4  16  22    1
5  25  31    4
6  36  42    9
7  49  55   16
EOD

f(x,a,b,c) = a*(x-b)**2 + c
colMin = 2
colMax = 4
set fit quiet nolog
array A[colMax]
array B[colMax]
array C[colMax]

do for [col=colMin:colMax] {
    a=1; b=1; c=1             # some initial values, sometimes 0 or NaN is not a good start
    fit f(x,a,b,c) $Data u 1:col via a,b,c
    A[col] = a;  B[col] = b;  C[col] = c
}

set key top left
plot for [col=colMin:colMax] $Data u 1:col w p pt 7 title sprintf("Column %d",col), \
     for [col=colMin:colMax] f(x,A[col],B[col],C[col]) w l \
          title sprintf("a=%.2f, b=%.2f, c=%.2f",A[col],B[col],C[col])
### end of code

Result: