Matrix Elements VB-800 Instrukcja Użytkownika Pobierz pdf (Strona 151)

A6.8 Expressions 143

Table A6.5 Result from operators involving an empty matrix as argument.

operator either argument empty both arguments empty

== FALSE TRUE

!= TRUE FALSE

>= FALSE TRUE

> FALSE FALSE

<= FALSE TRUE

< FALSE FALSE

other <> <>

A6.8.2 Postﬁx expressions

A6.8.2.1 Indexing vector and array types

Vector types (that is, string or matrix) are indexed by postﬁxing square brackets. A

matrix can have one or two indices, a string only one. In the case of two indices, they

are separated by a comma. If a matrix has more than one row or more than one column,

two indices must be used.

Note that indexing always starts at one. So a 2 × 3 matrix has elements:

[1,1] [1,2] [1,3]

[2,1] [2,2] [2,3]

Four ways of indexing are distinguished:

indexing type example

all elements m[.,.]

scalar m[1,1]

expression z={12}; m[1,z]

element-list m[1,1:2]

• A dot selects all elements (all rows for the ﬁrst index, all columns for the second).

• In the scalar indexing case (allowed for all non-scalar types), the expression in-

side square bracketsmust have scalar type, whereby double is convertedto integer

by discarding the fractional part.

If the index is scalar 0, all rows (ﬁrst index) or columns (second index) are used;

all elements if one index is used on a vector.

• An expression can be used for the index. If the expression evaluates to a a scalar,

it is identical to scalar indexing. If it evaluates to a matrix, all elements will be

used for indexing.

A matrix in the ﬁrst index selects rows, a matrix in the second index selects

columns. The resulting matrix is the intersection of those rows and columns.

• An index can be written as a space separated list of elements. Such elements

1 2 ... 146 147 148 149 150 151 152 153 154 155 156 ... 171 172

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