Axis 282 Uživatelský manuál stáhnout pdf (Strana 11)

Chapter II-12 — Graphs

II-243

folders containing data from a single run. All the waves in the chosen data folder whose names match the

names of waves displayed in the graph will replace the same-named waves in the graph.

You can also replace waves one at a time with any other wave. With the Replace All in Data Folder checkbox

unselected, choose a trace from the list below the menu. To replace the Y wave used by the trace, select the

Y checkbox; to replace the X wave select the X checkbox. You can replace both if you wish. Select the waves

to use as replacements from the menus to the right of the checkboxes. You can select _calculated_ from the

X wave menu to remove the X wave of an XY pair, converting it to a waveform display.

The menus allow you to select waves having lengths that don’t match the length of the corresponding X or

Y wave. In that case, use the edit boxes to the right to select a sub-range of the wave’s points. You can also

use these boxes to select a single row or column from a two-dimensional wave.

The dialog creates command lines using the ReplaceWave operation (page V-537).

Plotting NaNs and INFs

The data value of a wave is normally a finite number but can also be a NaN or an INF. NaN means “Not a

Number”, and INF means “infinity”. An expression returns the value NaN when it makes no sense math-

ematically. For example, log(-1) returns the value NaN. You can also set a point to NaN, using a table or

a wave assignment, to represent a missing value. An expression returns the value INF when it makes sense

mathematically but has no finite value. log(0) returns the value -INF.

Igor ignores NaNs and INFs when scaling a graph. If a wave in a graph is set to lines between points mode

then Igor draws lines toward an INF. By default, it draws no line to or from a NaN so a NaN acts like a

missing value. You can override the default, instructing Igor to draw lines through NaNs using the Gaps

checkbox in the Modify Trace Appearance dialog.

The following graph, generated by the wave assignments

wave1= log(abs(x-64)); wave1(40)=log(-1)

illustrate these points.

You can override the default, instructing Igor to draw lines through NaNs. See Gaps on page II-262 for details.

Scaling Graphs

Igor provides several ways of scaling waves in graphs. All of them allow you to control what sections of your

waves are displayed by setting the range of the graph’s axes. Each axis is either autoscaled or manually scaled.

Autoscaling

When you first create a graph all of its axes are in the autoscaling mode. This means that Igor automatically

adjusts the extent of the axes of the graph so that all of each wave in the graph is fully in view. If the data

in the waves changes, the axes are automatically rescaled so that all waves remain fully in view.

1.5

1.0

0.5

0.0

120100806040200

-INF at X = 64

NaN at X = 40

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 79 80

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Axis 282 Uživatelský manuál Strana 11