Y-axis visibility

[jbmagallanes]

i was trying to plot this function with varying q:

[Triple_S]

Ok, first of all you should get rid of the segmentation violation:
I’m 99% sure that it is cause by these three lines:

f1->SetTitle("Incident Beam Energy; Differential Cross Section");
f2->SetTitle("Incident Beam Energy; Differential Cross Section");
f3->SetTitle("Incident Beam Energy; Differential Cross Section");

The SetTitle function expects either a string of the format “tttt” with only the title of the function or “tttt;xxxx;yyyy” withthe title of the function and the title of the x and y axes. Your string is missing a semicolon for this definition which is probably the reason for the segmantation violation (char array index out of bounds, Why has C++ so useless error messages? )

It seems to me that you only wanted to set the x and y axes titles. This can be achieved this way:

f1->SetTitle(";Incident Beam Energy;Differential Cross Section");
f2->SetTitle(";Incident Beam Energy;Differential Cross Section");
f3->SetTitle(";Incident Beam Energy;Differential Cross Section");

Also see here:
https://root.cern.ch/doc/v614/classTF1.html#a3f80b00e53e6d0c262da34c254203f52

Afterwards your functions should be drawn with the gPad->SetLogy();s commented out. To fix these you should provide proper y ranges for logarhytmic sclale: Since exp(x) = 0 is either undefined or only valid for x = -inf your y-axis range must not include 0, otherwise the function cannot be drawn. I assume your function become negative at some point which is why root automatically choses a y-axis range that includes 0 which leads to the error.
You can fix this by setting the extremes manually:

f1->SetMinimum(1.e-5);
f1->SetMaximum(1.e2);
f2->SetMinimum(1.e-5);
f2->SetMaximum(1.e2);
f3->SetMinimum(1.e-5);
f3->SetMaximum(1.e2);

Of course you should adjust the values to reasonable ones (I don’t know your functions). After this the logarhytmic sclae should also work.

[Wile_E_Coyote]

Try with “23.0, 100.0” (instead of “0.0, 10.0”).

Note: You must make sure that you define a proper domain of your function (i.e. the denominator in your function must not be zero and the argument of the sqrt must not be negative).

BTW. @Triple_S ROOT is protected against empty / non-existent / misformed titles (or parts of them) so, you should not get any crashes. Also, in the majority of cases, it can automatically deal with non-positive values when asked for a log scale (unless you explicitly SetMinimum to be less or equal 0 or if all values are non-positive). Unfortunately, it is not protected against NaN nor Inf values.

[jbmagallanes]

yes, I tried this… but i guess there’s something wrong with my function… thanks
i’ll figure it out and go back to you when something goes wrong…

[jbmagallanes]

yes, it is expected to be infinite at 0.0 but i’ll figure it out… thanks
I will ask you later again later…