GNU Octave Manual Version 3 by John W. Eaton, David Bateman, Søren Hauberg Paperback (6"x9"), 568 pages ISBN 095461206X RRP £24.95 ($39.95) |
14.1.1 Terminal Output
Since Octave normally prints the value of an expression as soon as it has been evaluated, the simplest of all I/O functions is a simple expression. For example, the following expression will display the value of ‘pi’
pi -| pi = 3.1416
This works well as long as it is acceptable to have the name of the
variable (or ‘ans’) printed along with the value. To print the
value of a variable without printing its name, use the function
disp
.
The format
command offers some control over the way Octave prints
values with disp
and through the normal echoing mechanism.
- Automatic Variable: ans
- The most recently computed result that was not
explicitly assigned to a variable. For example, after the expression
3^2 + 4^2
is evaluated, the value returned by
ans
is 25.
- Built-in Function: disp (x)
- Display the value of x. For example,
disp ("The value of pi is:"), disp (pi) -| the value of pi is: -| 3.1416
Note that the output from
disp
always ends with a newline.If an output value is requested,
disp
prints nothing and returns the formatted output in a string.See also fdisp
- Command: format options
- Control the format of the output produced by
disp
and Octave's normal echoing mechanism. Valid options are listed in the following table.short
- Octave will try to print numbers with at least 5 significant figures within a field that is a maximum of 10 characters wide (not counting additional spacing that is added between columns of a matrix). If Octave is unable to format a matrix so that columns line up on the decimal point and all the numbers fit within the maximum field width, it switches to an ‘e’ format.
long
- Octave will try to print numbers with at least 15 significant figures within a field that is a maximum of 20 characters wide (not counting additional spacing that is added between columns of a matrix). As will the ‘short’ format, Octave will switch to an ‘e’ format if it is unable to format a matrix so that columns line up on the decimal point and all the numbers fit within the maximum field width.
long e
short e
-
The same as ‘format long’ or ‘format short’ but always display
output with an ‘e’ format. For example, with the ‘short e’
format,
pi
is displayed as3.14e+00
. long E
short E
-
The same as ‘format long e’ or ‘format short e’ but always
display output with an uppercase ‘E’ format. For example, with
the ‘long E’ format,
pi
is displayed as3.14159265358979E+00
. long g
short g
-
Choose between normal ‘long’ (or ‘short’) and
‘long e’ (or ‘short e’) formats based on the magnitude
of the number. For example, with the ‘short g’ format,
pi .^ [2; 4; 8; 16; 32]
is displayed asans = 9.8696 97.409 9488.5 9.0032e+07 8.1058e+15
long G
short G
-
The same as ‘format long g’ or ‘format short g’ but use an
uppercase ‘E’ format. For example, with the ‘short G’ format,
pi .^ [2; 4; 8; 16; 32]
is displayed asans = 9.8696 97.409 9488.5 9.0032E+07 8.1058E+15
free
none
- Print output in free format, without trying to line up columns of matrices on the decimal point. This also causes complex numbers to be formatted like this ‘(0.604194, 0.607088)’ instead of like this ‘0.60419 + 0.60709i’.
bank
- Print in a fixed format with two places to the right of the decimal point.
+
+ chars
plus
plus chars
-
Print a ‘+’ symbol for nonzero matrix elements and a space for zero
matrix elements. This format can be very useful for examining the
structure of a large matrix.
The optional argument chars specifies a list of 3 characters to use
for printing values greater than zero, less than zero and equal to zero.
For example, with the ‘+ "+-."’ format,
[1, 0, -1; -1, 0, 1]
is displayed asans = +.- -.+
native-hex
-
Print the hexadecimal representation numbers as they are stored in
memory. For example, on a workstation which stores 8 byte real values
in IEEE format with the least significant byte first, the value of
pi
when printed inhex
format is400921fb54442d18
. This format only works for numeric values. hex
-
The same as
native-hex
, but always print the most significant byte first. native-bit
-
Print the bit representation of numbers as stored in memory.
For example, the value of
pi
is01000000000010010010000111111011 01010100010001000010110100011000
(shown here in two 32 bit sections for typesetting purposes) when printed in bit format on a workstation which stores 8 byte real values in IEEE format with the least significant byte first. This format only works for numeric types. bit
-
The same as
native-bit
, but always print the most significant bits first. compact
- Remove extra blank space around column number labels.
loose
- Insert blank lines above and below column number labels (this is the default).
rat
- Print a rational approximation. That is the values are approximated by one small integer divided by another.
By default, Octave will try to print numbers with at least 5 significant figures within a field that is a maximum of 10 characters wide.
If Octave is unable to format a matrix so that columns line up on the decimal point and all the numbers fit within the maximum field width, it switches to an ‘e’ format.
If
format
is invoked without any options, the default format state is restored.
- Built-in Function: val = print_answer_id_name ()
- Built-in Function: old_val = print_answer_id_name (new_val)
- Query or set the internal variable that controls whether variable names are printed along with results produced by evaluating an expression.
ISBN 095461206X | GNU Octave Manual Version 3 | See the print edition |