Script round-up: calcsdnle

In THERMOCALC, versions up to and including the December 2020 release of TC 3.50, it is possible to print partial uncertainties (standard deviations) on calculated compositional variables and modes of phases. This is done using the script

calcsdnle yes

where the name of the script can be read as “calculate standard deviations on non-linear equations”.

When using this facility, it’s important to be aware that:

(1) The uncertainties that are printed are only those that stem from the dataset uncertainties. They do not include the uncertainties associated with the activity‚ąícomposition relations, or with end-members that are not taken from the dataset. The uncertainties that are not captured by the calcsdnle script are generally larger, or much larger, than the dataset uncertainties.

(2) The uncertainties associated with the different compositional variables and modes are correlated, although the correlations are not given in the output. The correlations may mean that, with a small change in the thermodynamic input, two isopleths might intersect in a very different region of P-T space, come to intersect in a plausible P-T window when they did not previously, or cease to intersect in a plausible P-T window when they did previously (this is a starting point for understanding the upcoming avPT+ approach to uncertainty analysis).