gnuplot-bugs

[Gnuplot-bugs] Gnuplot miscalculates formula badly

[ariadland <ari...@gm...>]

I plotted the following function in gnuplot (version 4.2   patch 5)

plot [.5:1.5] 1/(1/2.9898+94*(-x**2+1)**2*(-x**2+4/3)**2)  

The resulting figure should have two peaks.  One at x=1,  and one at about
x=1.2.  Gnuplot, however, just shows one smooth peak.

When I type in

plot [.5:1.5] 1/(1/2.9898+94*(-1.2**2+1)**2*(-1.2**2+4/3)**2)  

gnuplot returns a value that is horribly wrong  (checked by mathematica and
matlab).

Does it have something to do with the division?  I'm not sure,  but this is
a serious flaw.

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Re: [Gnuplot-bugs] Gnuplot miscalculates formula badly

[Hans-Bernhard B. <HBB...@t-...>]

ariadland wrote:
> I plotted the following function in gnuplot (version 4.2   patch 5)
> 
> plot [.5:1.5] 1/(1/2.9898+94*(-x**2+1)**2*(-x**2+4/3)**2)  
> 
> The resulting figure should have two peaks.  One at x=1,  and one at about
> x=1.2. 

What you want and what you told gnuplot to do doesn't match.  The 
problem, like just about every time this issue comes up, is that you 
missed paragraph 3 of "help expressions"

The function you want is

plot [.5:1.5] 1/(1/2.9898+94*(-x**2+1)**2*(-x**2+4.0/3)**2)

Re: [Gnuplot-bugs] Gnuplot miscalculates formula badly

[ariadland <ari...@gm...>]

Thanks.

I can't believe I missed that.  I am usually great with number types in
fortran.

Now I feel like an idiot.
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