MTDATA – Phase Diagram Software from the National Physical Laboratory

 

 

 

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Fitandplot

Introduction

The FITANDPLOT module allows data for a property that is dependent on temperature, or in principle any other variable, to be fitted automatically to a chosen function. The data comprise a sequence of pairs of numbers, the independent variable, normally temperature, and the dependent variable, for example the heat capacity, Cp. The default function is the conventional four-term Cp function. Although this handbook refers almost exclusively to fitting of heat capacity, more general use is not excluded. The data may relate to one or more phases of a substance. Several facilities are provided to aid in the fitting.

Plots and tabulations make clear exactly what ranges are being fitted and how well the function compares with the experimental results. Errors can be checked and amended data stored. Results from fits can be saved in a format ready to be loaded into a database.

Brief summary of commands

DEFINE The command DEFINE is used to define and input the data to be fitted. If the file is in the wrong FORMAT or no file exists then the input will be aborted.

LIST displays on the screen a numbered list of points, their weights and splits. Since points are identified by sequence number it is necessary to list the data to correlate the sequence and temperatures of individual points.

FIT causes automatic fitting of the data to the default or chosen FUNCTION to meet the default or chosen TOLERANCE. If necessary to meet the chosen TOLERANCE, additional ranges are automatically added. The first and penultimate points are weighted so as to ensure a good fit between the ranges. Results are rounded dependent on the function and can be REPORTed to the screen.

CHECK determines any errors in the data by a procedure for calculating differences. It has several sub-options which control how errors are detected. Suggested values for error points are shown on the screen and these can be used with AMEND to effect corrections.

WEIGHT The command WEIGHT is used to weight points according to their contribution to the fitting. The default weight is 1 for all points except the first and the last for the phase. Where automatic fitting requires another range the first and last but one point of each range is weighted to 10 unless a higher weight has been set manually. The maximum weight allowed is 20. The minimum weight is zero.

SPLIT causes forced splitting of ranges at user defined split points. The first and penultimate points of the new ranges are weighted to 10.

AMEND allows the user to amend values of data points specified by its sequence number.

SAVE_RESULTS saves the results of a fit to a file with default or chosen format.

STORE stores amended data

STATUS displays the current status of parameters such as tolerance, function, check order, and the destination of plots.

LASER sends a copy of any diagrams on file to a local plotting device if available.

RETURN takes the user out of FIT_AND_PLOT back to the module level.

<"Macro name"> runs a macro taken from a file. The name of the file should be entered in quotes. Commands can also be passed through to the operating system by prefixing them with a $ (dollar sign). The dollar sign and operating system command should be entered within quotes.

Further Information

A gentle introduction to using the options available in COPLOT contains annotated examples, each directed towards achieving a particular outcome and shows typical combination of commands which would be necessary to achieve that end.

A simple summary of the commands available can also be used as an index to obtain more detailed help about each command.

 

Updated 7 July 2010