Matrix Elements VB-800 Manuel d'utilisateur télécharger pdf (Page 162)

154 Appendix A7 Comparing Gauss and Ox syntax

A7.2.7 Declaration and constants

In Gauss, a variable can be assigned a

value with a let or implicit let state-

ment. If the variable doesn’t exist yet,

it is declared, otherwise it is redeclared.

A variable can be declared explicitly with

the declare statement. Assignment in

a let statement may consist of a number,

a sequence of numbers (or strings) sepa-

rated by spaces, or numbers in closed in

curly brackets. The latter speciﬁes a ma-

trix, with a comma separating rows, and

a space between elements in a row (these

are not proper matrix constants, because

they cannot be used in expressions). A

variable outside a function is also created

if a value is assigned to it (and it doesn’t

exist yet).

letw={111};

let y0 = 1 2;

let y1[2,2] = 1 1 2 2;

y2[2,2] = {1 1, 2 2}; /*(1)*/

let w[2,2] = 1;

let w[2,2];

w = zeros(2,2);

The line labelled (1) is an implicit let

which creates a 2 × 2 matrix. A state-

ment like y2[2,2] = 1; on the other

hand puts the value one in the 2,2 posi-

tion of y, which therefore must already

exist.

Ox has explicit declaration of variables.

A value can be assigned to a variable at

the same time as it is declared. If the vari-

able has external scope (i.e. is assigned

outside any function), you can use con-

stants only, (matrix or other constants).

Such constants can also be used in ex-

pressions.

decl w = < 1,1,1 >;

decl y0 = <1,2>;

decl y1 = <1,1; 2,2>;

decl y2 = <1,1; 2,2>;

decl w[2][2] = 1;

decl w[2][2];

decl w = zeros(2, 2);

/* only inside function */

If all statements would be used together,

the compiler would complain about the

last three declarations: w was already de-

clared earlier (no redeclaration is possi-

ble, but re-assignment is, of course). The

last declaration involves code, and can

only be made inside a function.

A7.2.8 Expressions

Assignment statements are quite similar,

e.g. y=a.*b+3-d;works in

both Gauss and Ox, whether the variables

are matrices or scalars.

Ox allows multiple assigments, e.g. i=

j=0;. In addition there are conditional

and dot-conditional expressions.

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