Error "Bad Numerical Expression k"

I want to draw these functions graph
fik and
psik
I am using TF1 and I write this code

TF1 *tf1 = new TF1(“graph”,“exp(-k)”,0.0,0.5); for graph 1 but I have error which bad numerical expression k
How can I write code for this graph

Try

TF1 *tf1 = new TF1("graph","exp(-1.*[0]*TMath::Abs(x))",0.0,0.5);

I tried but I think result is not true

Maybe your [0] (the b parameter from your original example) is set to 0? That would explain it. Try setting it to something different with SetParameter().

setParameter Can you give example I am cnfused a bit

In your case,

tf1->SetParameter(0, 10);

will set the [0] to 10.

Thanks I think it is Ok this time


and I try my second graph now

TF1 ref guide explains all this very clearly:
https://root.cern/doc/master/classTF1.html

I tried my second graph like this

TF1 * f2 = new TF1(“graph” ,"(1.[0]TMath::Abs(x)/90.0)(1/xx+b[0]*TMath::Abs(x)b[0]*TMath::Abs(x))",0.0,0.5);

but again I have numerical error ?

Why do you have Abs(x) this time? And why do you have b in the code?
TF1* tf2 = new TF1("graph2", "[0]/(TMath::Pi() * (x*x+[0]*[0]))", 0., 0.5)

oov I am sorry Thank you

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