Syntax

DO <xrefin-do-statement>

is invoked as an xrefin statement. Action takes place as soon as the construct is complete.

<xrefin-do-statement>:==

<xrefin-do-mode> ( <xrefin-property> = <xrefin-do-expression> )

<xrefin-do-mode>:==

AMPLitude

carries out an operation using amplitudes of xrefin properties.

COMPlex

carries out an operation in complex space.

PHASe

carries out an operation using phases of xrefin properties. Phases are manipulated in degrees.

SCALe

    involves an operation that multiplies the left-hand side (lhs) by a scale factor k, which is defined as

where rhs represents the right-hand side of the equation. The action of this statement is identical to the scaling carried out when computing the R value or the residual (cf. Eqs. 12.1, 12.6), except that it refers the scaling to the right-hand side of the equation, whereas in the residual or R value evaluation the scaling refers to . Therefore, if the right-hand side of the scaling operation consists of , the program refers only to but not to to .

<xrefin-do-expression>:==

<xrefin-vflc> [ <op>
<xrefin-do-expression> ] represents a mathematical operation and is defined in Section 2.16.

<xrefin-vflc>:==

<function>

| <xrefin-function> | <symbol> | <real> | <integer> | <complex> | <xrefin-property> represents mathematical functions and is defined in Section 2.16. Special xrefin functions are defined below. The data type of the function arguments has to match the data type of the operands.

<xrefin-property>:==

FCALC

specifies calculated structure factors (complex).

FOBS

specifies observed structure factors (complex).

FPART

specifies partial structure factors (complex).

SIGMA

specifies values (real).

TEST

is an array for cross-validation that allows one to compute the free R value (see Chapter 15).

WEIGHT

specifies weights (real).

<xrefin-function>:==

H()

defines an array that consists of the Miller index h.

K()

defines an array that consists of the Miller index k.

L()

defines an array that consists of the Miller index l.

S()

defines an array that consists of the length of the reciprocal lattice vector for each reflection h,k,l.