Basically I want to use PGFplots/tikzs to plot the sum of two expressions, but the first expression - let's name it `f(x)` - is specified within `0<=x<=1000` and the second expression - let's name it `g(x)` - should only be specified within `100<=x<=200` but is unfortunately not equal zero in the regions outside of `100<=x<=200`. I just want to add the two functions `(f(x)+g(x))` and plot the result with a single `\addplot` command within the full domain `0<=x<=1000`, with `g(x)` being zero outside of `100<=x<=200`.

Do you know a flexible and easy way to achieve the desired bahavior with a single `\addplot[...][domain=0:1000]{...}` command, as the only solution I found (but some sort of don't like - as it forces me to plot three different functions) is plotting

```
1. \addplot ... f(domain: 0<=x<100)
2. \addplot ... f(domain: 200<x<=1000)
3. \addplot ... f+g(domain: 100<=x<=200)

```

as a workaround.

PS: I want to avoid solutions that involve gnuplot or having to store the data within files or something like that... I'd prefer to have a solution that works with the following packages/libraries within the preamble `\usepackage{tikz,pgfplots,grffile,amsmath}` and `\usetikzlibrary{fpu}` but feel free to post the most easy solution.

I hope you don't mind that I didn't include any MWE and that the syntax I provided within the description is actually not 'fully working syntax' but just some sort of symbolic excerpts that provide the key to understand my problem.