Procedures | <Prev Next> |

Loomis Wood style plots can be produced with `PGOPHER`;
they work by plotting the same spectrum several times, with
successive spectra horizontally displaced by an amount given by a
function in terms of the plot number, *m*. With the correct
choice of function (typically a polynomial), successive
transitions in a branch will appear lined up.

This is done by adding a Loomis Wood object in
the Overlays window (brought up
with "`View, Overlays`"); they can be created at the top
level (in which case multiple windows are created) or under a
specific plot, in which case the plot is duplicated in a single
window. Right click on the top level object or the specific plot
as required, and select "`Add New...`", "`Loomis Wood`".
The required function is given in the comment in terms of the
running plot number, *m*. The default polynomial is:

but any sensible function ofb(m-m_{Lowest}) +d(m-m_{Lowest})^{2}

To determine the parameters of the function a built in fitting
process can be used, similar to that used for calibrating spectra. A Loomis Wood
window can be brought up by right clicking on the Loomis-Wood
object, and selecting "`View...`". When this is visible,
and selecting an active Loomis-Wood object, a series of peaks
making up a branch can be measured. Right clicking and dragging
over a peak will add the peak to the series for that object,
with the *m* value set according to the spectrum the peak
is measured in. Pressing "Fit" will do a least squares fit on
the parameters in the function using the given peaks, and then
update the display to reflect the new parameters. To avoid
undesirable correlation in the parameters of the function, the
values fitted to are offsets from the position of the peak with
the lowest value of *m*. The `mLowest` parameter
(and the corresponding variable in the expression) is set to
this value of *m* at the start of the fit. Other
operations in the Loomis-Wood window include:

- The up and down arrows increment and decrement by one all the m values in the peak list, to allow assignments to be adjusted.
- The polynomial setting can be used to change the function to a polynomial of the given order; to use a more general function or constrain parameters use the non-linear fit dialog obtained by pressing the adjacent button.
- Changing the
`moffset`value sets the m offset for the Loomis Wood object, and also shifts the main display so that the peak for which*m*=*m*_{Offset}is at the centre of the display. This can be used to walk backwards and forwards along a branch. `Other..., Copy for``BranchExpr`copies the selected measurements to the clipboard, suitable for line list fitting using the BranchExpr directive. This allows the specification of the conversion of the running number,*m*, to branch labels to be specified in a general way.

Active |
True to produce a Loomis-Wood plot; there can be multiple
Loomis-Wood objects, but only one should be active at a
time. |

nDebug |
If non zero, write the values of all the variables and the value of the function on each evaluation to the log window. See debugging for options on the output. |

nPlots |
The number of plots to produce |

mOffset |
The m values used in the plots are displaced by
this. The plots have m values of mOffset
to mOffset+nPlots-1. |

ShrinkSimulation |
If false, the simulation occupies half the
plot. If false, the simulation shrinks to 1/(nPlots+1)
of the plot. |

ShowProduct |
For future functionality |