SasView: Ticket #396: allow density from formula in sld calculator
http://trac.sasview.org/ticket/396
<p>
The following formula is a 20:80 volume ratio of H2O:D2O, where D2O is assumed to have the same number density as H2O, but with isotopic substitution of D for H:
</p>
<blockquote>
<p>
20%vol H2O@1n <em> D20@1n
</em></p>
</blockquote>
<p>
The resulting formula has a known number density, so the SLD calculator should be able to ask the formula for the density rather than requiring the user to calculate it.
</p>
en-usTrac 1.0.1