/ 
Finance-Shares-1.03
/ Finance::Shares::gradient

NAME

Finance::Shares::gradient - Smoothed rate of change

SYNOPSIS

Two examples of how to specify a gradient line, one showing the minimum required and the other illustrating all the possible fields.

    use Finance::Shares::Model;
    use Finance::Shares::gradient;

    my @spec = (
	...
	lines => [
	    ...
	    minimal => {
		function => 'gradient',
	    },
	    full = {
		function => 'gradient',
		graph    => 'Stock Prices',
		gtype    => 'price',
		line     => 'some_line',
		period   => 10,
		strict   => 1,
		key      => '10 day gradient',
		style    => { ... },
		shown    => 1,
		order    => -99,
	    },
	    ...
	],
	...
	samples => [
	    ...
	    one => {
		lines => ['full', 'minimal'],
		...
	    }
	],
    );

    my $fsm = new Finance::Shares::Model( @spec );
    $fsm->build();

DESCRIPTION

Momentum is calulcated as the difference in value between now and N periods in the past. This module calulates an average momentum for those N periods.

Strictly, this should be from -N/2 to +N/2 but then the line is undefined at its most recent edge. As this is rarely useful, the default is to use the more normal -N to 0. Note that the end section is not accurate - it gives an idea but it may be wrong. (So what's new in stock price forecasting?)

When period is 1, the gradient line is a resonable approximation to the rate of change of the source.

The results are normally displayed on an 'analysis' graph as the changes may be positive or negative values. WARNING: if you specify a graph for the gradient line, it will NOT relate to the Y axis. '0' will probably be around the middle (vertically) of the gradient line, while for the Y axis, '0' may well be below the bottom of the page.

To be any use, there must be a Finance::Shares::Model specification lines entry that has a function field declaring the module's name. Then the entry's tag must be used by a sample in some way. This may be either directly in a line field, or by referring to it within a test.

The other main fields are line and period.

OPTIONS

function

Required. Must be gradient.

graph

If present, this should be a tag declared as a charts resource. It identifies a particular graph within a chart page. A gtype is implied. (No default)

gtype

Required, unless graph is given. This specifies the type of graph the function lines should appear on. It should be one of price, volume, analysis or logic. (Default: price)

line

Identifies the line whose data is to be considered. (Default: 'close')

period

The number of values to use. The actual time will depend on the dates by field. (Default: 5)

Normally at least this number of dates will have been read in before the first date shown on the chart. However, a small initial gap may be visible if some of that working data was missing. Set the dates before field to adjust this.

strict

Set this to 1 to get the more accurate, but possibly less useful, spread using -N/2 to +N/2 periods. (Default: 0)

key

Most functions generate suitable (if lengthy) entries. This provides the opportunity to identify the line in the Key panel, next to the style.

order

The entries on the graph are sorted according to this value, which defaults to the order required for calculation. A large integer will bring the line to the front and a negative number will put it behind all the rest.

Examples

-1

The line goes behind the data.

0.5

In front of the data, but only just.

999

Probably the top line.

shown

1 for the line to be shown, 0 hides it. (Default: 1)

style

This is normally a hash ref defining the data's appearance. See PostScript::Graph::Style for full details, or "Lines" in Finance::Shares::Model for an example.

BUGS

Please let me know when you suspect something isn't right. A short script working from a CSV file demonstrating the problem would be very helpful.

AUTHOR

Chris Willmot, chris@willmot.org.uk

LICENCE

Copyright (c) 2002-2003 Christopher P Willmot

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. A copy can be found at http://www.gnu.org/copyleft/gpl.html

SEE ALSO

Finance::Shares::Overview provides an introduction to the suite, and fsmodel is the principal script.

Modules involved in processing the model include Finance::Shares::Model, Finance::Shares::MySQL, Finance::Shares::Chart. Chart and file details may be found in PostScript::File, PostScript::Graph::Paper, PostScript::Graph::Key, PostScript::Graph::Style.

All functions are invoked from their own modules, all with lower-case names such as Finance::Shares::moving_average. The nitty-gritty on how to write each line specification are found there.

The quote data is stored in a Finance::Shares::data object. For information on writing additional line functions see Finance::Share::Function and Finance::Share::Line. Also, Finance::Share::test covers writing your own tests.

1 POD Error

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