To make a density map from a 2D set of data, the first step is to compute values for the third dimension. (Gnuplot has no facilities for computing these values automatically.) The simplest way is to make a 2D histogram; the plot is divided in small 2D regions, and the z-values are proportional to the number of points inside these regions. The following Python script will make an histogram from a time series of two dihedral angles.
PyQuante is an open-source suite of programs for developing quantum chemistry methods. The program is written in the Python programming language, but has many "rate-determining" modules also written in C for speed.
SensoTech is a leading supplier of process analyzers for the in-line measurement of concentration and density in liquid processes. Typical further applications are the phase interface detection or the monitoring of complete chemical reactions like polymerisation or crystallization.
Twice today that question was put to me. I thought I’d take a moment and answer it not just for the two individuals who asked, but for anyone who might be wondering. Below is my recommendation…
Geophysical Research Letters publishes short, concise research letters that present scientific advances that are likely to have immediate influence on the research of other investigators. GRL letters can focus on a specific discipline or apply broadly to the geophysical science community.
R. Bommakanti, G. Bokoch, J. Tolley, R. Schreiber, D. Siemsen, K. Klotz, and A. Jesaitis. J Biol Chem, 267 (11):
7576-81(April 1992)Bommakanti, R K Bokoch, G M Tolley, J O Schreiber, R E Siemsen, D
W Klotz, K N Jesaitis, A J R01-AI22735/AI/NIAID NIH HHS/United States
R01-GM39434/GM/NIGMS NIH HHS/United States Research Support, Non-U.S.
Gov't Research Support, U.S. Gov't, P.H.S. United states The Journal
of biological chemistry J Biol Chem. 1992 Apr 15;267(11):7576-81..