TGraph constructor and plotting

ROOT
1

Hi,
I want to read in a data file (5 columns) and I have been trying to use the following constructor:
TGraph(const char* filename, const char* format = “”%lg %lg"", Option_t* option = “”"")
I tried using it on the ROOT command prompt (instead of writing a script) just so I may learn whether I am using the command properly. I used the basic:
TGraph *g = new TGraph(“fname.dat”)
how can I access the data to make sure this works and how can I get it to plot? I have tried g->Print() just to see if the data is being read but to no avail.
Thank you.

2

If your file fname.dat is readable and contains at least 2 columns of numbers, what you do should work. More details please.

Rene

3

Hi,
My file is readable I am sure of it cause I can call it for making an ntuple and draw histograms. There are 5 columns of data. I just cant see how I may call TGraph in such a way that I can access the data. Is the following valid?
TGraph *g = new TGraph(“fname.dat”, “x y z t”)
I thought this way I was setting x to be column one and so on. This command gives me no errors. Then is it valid to say:
g->DrawGraph(x) ? (Apparently not but I dont know where I am going wrong).
Thank you.

4

Hi,
an update:
I have noticed that the following:
TGraph *g = new TGraph(“fname.dat”)
only reads in the first two colmns (instead of 5) from the file. How do I get it to read all five?
Thank you.

5

TGraph is a class dealing with two vectors X and Y.

So, do not expect that you will have the x y z t vectors as this quote suggested.

It would be very helpful if you send a small macro (and data) showing what you are doing. But remember, TGraph has only 2 vectors !

6

Hi,
attached are the data file and the script I am invoking.
What I am trying to do is to plot a graph of the 2nd, 3rd, 4th and 5th column vs the 1st, seperately. Finally I would also like to plot a 3D graph of the 2nd, 3rd and 4th columns. I would appracite any suggestions on how to deal with this.
Thank you very much.
Best Regards…
ode45.txt (2.38 KB)
ode45draw.C (248 Bytes)

7

Seems to me the best way is to read the file in 5 vectors: x y z t u
and then make all the TGraphs you need combining the vectors as you wish.