Volume 2 Chapter 3 3D-Constrain Sub-menu SELECT

Function

SELECT is used to specify the allowed minimum and maximum values for a parameter which has already been defined using the DEFINE PARAMETER or TRANSFORM commands.

Only if the value of the parameter lies within this range will the crystal fragment be accepted as a hit.

QUEST3D applies the selection criteria in the order input by the user.

Example

Suppose that we have defined parameter B1 as the distance between atoms 8 and 7.

Select SELECT

Select or type items for SELECT. If necessary reselect SELECT to
end input.
Select CANCEL to cancel command.

Select or type B1

Type limiting values for B1 (separated by space or
comma)

Type 6.0 8.0 <RETURN>
In the summary area we now have:
```
B1   6.0   8.0
```
The line is displayed in yellow to indicate that it is a SELECT command.
In the dialogue area we now have the "home" prompt:
```
Search for ALL crystal fragments
OVERLAP of crystal fragments permitted
Select a menu command or TO-BUILD to return to the BUILD menu.
```
The resultant command in the instruction document is:
```
SELECT  B1  6.0  8.0
```

Note the following:

Type limiting values for B1 (separated by space or
comma)

Type 8.0 6.0 <RETURN>

Beep
*SELCHK*  Range must be MIN followed by MAX and MIN < MAX.
Please press <RETURN> to continue.  Thank you.

Notes

When specifying the limiting values real numbers or integers may be used.
When specifying limiting values for a torsion angle the following rules apply:
The torsion angle A-B-C-D is the angle by which the vector A-B must be rotated to overlie the vector C-D when viewed along the vector B-C from B to C.
According to the convention of Klyne and Prelog (Experientia 16, 521, 1960):
- a clockwise rotation is positive
- an anti-clockwise rotation is negative.
The selection range for a torsion angle parameter is interpreted by QUEST as including those torsion angles within the segment formed by a clockwise rotation from the first limiting value to the second.
Limiting values must be specified with the second value greater than the first, eg. -160 -140
Special care should be taken when specifying limiting values for:
- angle between two vectors
- angle between a vector and a plane
- angle between two planes
One cannot predict in advance whether the calculated angle will be the "expected" value or its supplement. To cater for this situation one might choose to obtain the acute value in all cases.
Suppose the defined angle has been named ?ANG
Using TRANSFORM

set ?SIN = SIN ?ANG
set ACUTE = ASIN ?SIN

where ?SIN is the sine of ?ANG, ACUTE is the arcsine of ?SIN.
Apply the SELECT limiting values to ACUTE.
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Volume 2 Chapter 3 3D-Constrain Sub-menu CENTROID .