Hi, I’m a newbie and I’ve been trying to graph a set of data written in a txt file.
I think Everything has been set up correctly in my program yet whenever I run it on root with .x function, it gives me as a feedback an error message and subsequently ends itself:
Blockquote
root [0] .x rl.C
Assertion failed: isSingleDecl() && “Isn’t a single decl”, file C:\build\ws\BUILDTYPE\Release\LABEL\windows10\V\6-18\root\interpreter\llvm\src\tools\clang\include\clang/AST/DeclGroup.h, line 87
What I’m trying to do is graph my data and also set my error bars. My program is here:
{
double t=0, Vl=0, Vr=0;
myGraph1 = new TGraphErrors("Vl.txt");
myGraph1->SetPoint(myGraph1->GetN(), t, Vl);
myGraph1->SetPointError(myGraph1->GetN()-1, 0, 0.1);
myGraph1->SetMarkerStyle(21);
myGraph1->SetMarkerSize(0.8);
myGraph1->SetLineColor(kBlue+1);
myGraph1->SetTitle("Caratterizzazione di un circuito RL; Tempo [ms]; Potenziale V [V] ");
myGraph1->Draw("AP");
mygraph2 = new TGraphErrors("Vr.txt");
myGraph2->SetPoint(myGraph2->GetN(), t, Vr);
myGraph2->SetPointError(myGraph2->GetN()-1, 0, 0.1);
ci = TColor::GetColor("#66cccc");
myGraph2->SetMarkerStyle(23);
myGraph2->SetMarkerSize(0.8);
myGraph2->SetMarkerColor(ci);
myGraph2->SetLineColor(kBlue+1);
myGraph2->Draw("P Same");
}
Hope someone can help me, thank you very much in advance.
_
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ROOT Version: Not Provided
Platform: Not Provided
Compiler: Not Provided
Try with:
auto myGraph1 = new ...
auto myGraph2 = new ...
auto ci = ...
if you mean implementing it like this:
{
double t=0, Vl=0, Vr=0;
auto myGraph1 = new TGraphErrors("Vl.txt");
myGraph1->SetPoint(myGraph1->GetN(), 0, 0);
myGraph1->SetPointError(myGraph1->GetN()-1, 0, 0.1);
myGraph1->SetMarkerStyle(21);
myGraph1->SetMarkerSize(0.8);
myGraph1->SetLineColor(kBlue+1);
myGraph1->SetTitle("Caratterizzazione di un circuito RL; Tempo [ms]; Potenziale V [V] ");
myGraph1->Draw("AP");
auto mygraph2 = new TGraphErrors("Vr.txt");
myGraph2->SetPoint(myGraph2->GetN(), 0, 0);
myGraph2->SetPointError(myGraph2->GetN()-1, 0, 0.1);
auto ci = TColor::GetColor("#66cccc");
myGraph2->SetMarkerStyle(23);
myGraph2->SetMarkerSize(0.8);
myGraph2->SetMarkerColor(ci);
myGraph2->SetLineColor(kBlue+1);
myGraph2->Draw("Same");
}
I tried, yet it still gives me the same error 
Try with:
TGraphErrors *myGraph1 = new ...
TGraphErrors *myGraph2 = new ...
Int_t ci = ...
Note that you sometimes use “mygraph...” and sometimes “myGraph...”.
Also, graphs do not have the “SAME” draw option at all (it’s not needed).
It somehow fixed by itself? I am so confused. Yet another problem persists, it doesn’t show me any bar errors.
{
t=0, Vl=0, Vr=0;
myGraph1 = new TGraphErrors("843931.txt", "%lg %lg %*lg");
myGraph1->SetPoint(myGraph1->GetN(), t, Vl);
myGraph1->SetPointError(myGraph1->GetN()-1, 0, 0.1);
myGraph1->SetMarkerStyle(21);
myGraph1->SetMarkerSize(0.8);
myGraph1->SetLineColor(kBlue+1);
myGraph1->SetTitle("Caratterizzazione di un circuito RL; Tempo [ms]; Potenziale V [V] ");
myGraph1->Draw("AP");
myGraph2 = new TGraphErrors("843931.txt", "%lg %*lg %lg");
myGraph2->SetPoint(myGraph2->GetN(), t, Vr);
myGraph2->SetPointError(myGraph2->GetN()-1, 0, 0.1);
ci = TColor::GetColor("#66cccc");
myGraph2->SetMarkerStyle(23);
myGraph2->SetMarkerSize(0.8);
myGraph2->SetMarkerColor(ci);
myGraph2->SetLineColor(kBlue+1);
myGraph2->Draw("P");
}
You do not read errors from your data file.
I am not trying to read them, infact I am trying to associate a fixed Error to the data that my program is reading from the txt file
Thank you so much for your help btw 
You need to loop over all points and set an error for each of them.
So i need to create a while(true), read from the files and set the error right?
No, after you have all points read, just add a for loop which sets errors to your desired value.
for (int i = 0; i < myGraph1->GetN(); i++) myGraph1->SetPointError(i, 0., 0.1);
1 Like
That fixed it! I read the macro and the way it was setup it set my error as 0 non stop.
Thank you so much!
