A continuous random variable $X$ is defined in a domain $A$ which is the union of two non-overlaping subdomains $B$ and $C$. When analysing the distribution of $X$, one could calculate the PDF of $X$ considering the whole domain $A$, or two PDFs, one for each subdomain separately.
It proved more useful to calculate two functions, one for each subdomain, normalized in such a way that the integral of each function equals the relative size of the subdomain to the whole domain. The sum of these two functions is a PDF, but not each one individually. Is there a name for such a function?