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VE[ctor] C[lear]....clears all current vector elements, whether switched on or off.

See also : VECTOR, VECTOR DELETE, VECTOR OFF, VECTOR ON

You plot vectors by means of the VECTOR command, which has the form:

VE[ctors] <plane> <number> <subregion>

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VE[ctor] D[elete]....deletes the last vector element, whether it is switched on or off.

See also : VECTOR, VECTOR CLEAR, VECTOR OFF, VECTOR ON

When you plot vectors, a key appears on the plot, which consists of a vector arrow together with its magnitude and units. When you plot shaded vectors, the key also contains information about the colours used for shading. The length of the vector key arrow is fixed. The velocity it represents is set by the SET VECTOR REFERENCE command.

The SET VECTOR KEY command governs the display of the scaling information.

The SET VECTOR UNITS command enables you to specify the units of the vector key.

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[Vector No] is the sequence number of the VECTOR element in the stack. Typing in any valid number (<the total number of VECTOR element>) will pop up the corresponding VECTOR element and make it become the current element.

Only the attributes of the current VECTOR element can be modified.

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VE[ctor] OF[f] <element range>....switches off the specified vector element(s), which will not appear in subsequent plots until it has been switched on again.

See also : VECTOR, VECTOR DELETE, VECTOR CLEAR, VECTOR ON

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VE[ctor] ON <element range>....switches on the specified vector element(s), which will appear in subsequent plots.

See also : VECTOR, VECTOR DELETE, VECTOR OFF, VECTOR CLEAR

You use the options DASH and COLOUR for vectors in the same way as for grids. The SHADE option colours the vector arrows, according to magnitude, from blue (low values) to red (high values).

An example of a vector command with optional parameters is:

VEC IX 1 IY 1 3 DASH 2 SHADE

which plots coloured and dashed vectors, on the IX=1 plane, over the patch IY=1 to 3 and IZ=1 to M.

You may plot vector arrows in one of two ways. They may be centred at the cell nodes; or their tails can start at the cell nodes (the default). The commands SET VECTOR CENTRE ON and SET VECTOR CENTRE OFF switch between these two plotting modes.

PHOTON automatically calculates a reference velocity for plotting vectors. You may wish to reset this value to one having special significance, or to make the vector arrows appear smaller or larger. This can be done through the command:

SET VECTOR REFERENCE <n>

where <n> is the reference-velocity value required. If no value is given, PHOTON displays the existing value and prompts you for a new value. Pressing <Return> causes PHOTON to recalculate a suitable reference velocity automatically.

A fully-VECTORisable linear-equation solver, especially suitable for Cray and Convex machines, has replaced the previous partially- vectorisable version. Speed-up factors in excess of 2 have been obtained. The new solver produces some speed-up also for scalar machines.

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VE[ctors] <plane> <number> <subregion> <options>.... will plot vector information over the whole or a subregion of a specified plane. A subregion consists of the extent of the grid in the other two coordinate directions, and either or both may be omitted if the total extent in that direction is to be used.

For example, VEC Y 1 X 3 5 Z 7 M will plot vectors on the Y 1 plane, over the region X cells 3 to 5, Z cells 7 to the maximum.

Options for vector plotting are DASH <number>, which will set the linetype of the vectors to dashed. Values may be between 1 and 3; COLOUR <number>, which will draw the vectors coloured, the colour lying between 0 and 15; SHADE, which will produce coloured contours, ranging from blue (low values) to red (high values).

Vector arrows are scaled relative to the current reference velocity. This is prompted for by PHOTON when the first set of vectors is plotted, and may be subsequently changed by use of the TYPVEC command.

Vector arrows may be positioned relative to the cell centres in one of two orientations - see VCEN for details.

Other vector quantities may be plotted apart from the first- phase velocities - see SET VECTOR PHASE and SET VECTOR COMPONENTS for details.

NOTE that a 'fields' file (PHI) is necessary for vector plotting.

See also : VECTOR CLEAR, VECTOR DELETE, VECTOR OFF, VECTOR ON, SET VECTOR KEY, SET VECTOR CENTRE, SET VECTOR PHASE, SET VECTOR COMPONENTS, SET VECTOR REFERENCE, SET VECTOR BOUNDARY SET VECTOR AVERAGE, SET VECTOR KEY

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[Vectors] activates the vector sub-menu to set a new vector element to be drawn.

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