|
{
"cells": [
{
"cell_type": "markdown",
"id": "1023ec3f",
"metadata": {},
"source": [
"### Variables and Objects\n",
"In GAP (and most other programming languages), constants always have the same meaning. On the other side of things are variables, which have an associated identifier and a meaning that depends on what has been assigned to them.\n",
"\n",
"Assignments are done in GAP using the `:=` operator, with the identifier of the variable on the left and the value/object to be assigned on the right. Almost any GAP object can be assigned to a variable. After assignment, the variable will evalute to that object if evaluated. As such, it is possible to refer to the object by the name of the variable in any situation:"
]
},
{
"cell_type": "code",
"execution_count": 3,
"id": "f25c63ce",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"2"
]
},
"execution_count": 3,
"metadata": {
"text/plain": ""
},
"output_type": "execute_result"
}
],
"source": [
"a := 9 - 7;"
]
},
{
"cell_type": "code",
"execution_count": 4,
"id": "7379987a",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"6"
]
},
"execution_count": 4,
"metadata": {
"text/plain": ""
},
"output_type": "execute_result"
}
],
"source": [
"a + 4;"
]
},
{
"cell_type": "markdown",
"id": "62762ac2",
"metadata": {},
"source": [
"After an assignment, the value/object of the assigned variable is printed. This printing can be prevented by doubling up the semicolon at the end of the assignment command:"
]
},
{
"cell_type": "code",
"execution_count": 5,
"id": "44d0f53f",
"metadata": {},
"outputs": [],
"source": [
"b := 22;;"
]
},
{
"cell_type": "markdown",
"id": "361d9381",
"metadata": {},
"source": [
"In Jupyter, variable assignments are kept across cells. As such, the variables defined earlier will be accessible in cells run after, and can be accessed or reassigned as necessary."
]
},
{
"cell_type": "code",
"execution_count": 6,
"id": "83f675ff",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"24"
]
},
"execution_count": 6,
"metadata": {
"text/plain": ""
},
"output_type": "execute_result"
}
],
"source": [
"a + b;"
]
},
{
"cell_type": "markdown",
"id": "eb591787",
"metadata": {},
"source": [
"GAP also contains a number of pre-defined variables. You can get an overview of all the current variables in GAP by entering the function `NamesGVars()`. Many of these are predefined by the GAP kernel:"
]
},
{
"cell_type": "code",
"execution_count": 7,
"id": "2306161f",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
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]
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