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colon, :

Create vectors, array subscripting

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Syntax

y = j:k
y = j:i:k

Description

y = j:k returns a regularly-spaced vector, [j, j+1 ,..., k]. j:k is empty when j > k.

At least one of the colon operands must be a fi object. All colon operands must have integer values. All the fixed-point operands must be binary-point scaled. Slope-bias scaling is not supported. If any of the operands is complex, the colon function generates a warning and uses only the real part of the operands.

y = colon(j,k) is the same as y = j:k.

example

y = j:i:k returns a regularly-spaced vector, [j,j+i,j+2i, ...,j+m*i], where m = fix((k-j)/i). y = j:i:k returns an empty matrix wheni == 0, i > 0 and j > k, or i < 0 and j < k.

example

Examples

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Open Live Script

When you use fi as a colon operator, all colon operands must have integer values.

a = fi(1,0,3,0);	
b = fi(2,0,8,0);	
c = fi(12,0,8,0);	
x = a:b:c
x = 
     1     3     5     7     9    11

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Unsigned
            WordLength: 8
        FractionLength: 0

Because all the input operands are unsigned, x is unsigned and the word length is 8. The fraction length of the resulting vector is always 0.

Open Live Script
a= fi(int8(-1));
b = uint8(255);
c = a:b;
len = c.WordLength
len = 
9

signedness = c.Signedness
signedness = 
'Signed'

The word length of c requires an additional bit to handle the intersection of the ranges of int8 and uint8. The data type of c is signed because the operand a is signed.

Open Live Script

If the beginning and ending operands are unsigned, the increment operand can be negative. 

x = fi(4,false):-1:1
x = 
     4     3     2     1

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Unsigned
            WordLength: 16
        FractionLength: 0
Open Live Script

If any of the operands is floating-point, the output has the same word length and signedness as the fi operand

x = fi(1):10
x = 
     1     2     3     4     5     6     7     8     9    10

          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 16
        FractionLength: 0

x = fi(1):10 is equivalent to fi(1:10, true, 16, 0) so x is signed and its word length is 16 bits.

If your code uses non-integer operands, rewrite the colon expression so that the operands are integers.

The following code does not work because the colon operands are not integer values.

Fs = fi(100);
n = 1000;
t  = (0:1/Fs:(n/Fs - 1/Fs));

Rewrite the colon expression to use integer operands.

Fs = fi(100);
n = 1000;
t  = (0:(n-1))/Fs;

If the value of any of the colon operands is outside the range of the data type used in the colon expression, MATLAB® generates an error.

    y = fi(1,true,8,0):256

MATLAB generates an error because 256 is outside the range of fi(1,true, 8,0). This behavior matches the behavior for built-in integers. For example, y = int8(1):256 generates the same error.

Input Arguments

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Beginning operand, specified as a real scalar integer-valued fi object or built-in numeric type.

If you specify non-scalar arrays, MATLAB interprets j:i:k as j(1):i(1):k(1).

Data Types: fi |single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Increment, specified as a real scalar integer-valued fi object or built-in numeric type. Even if the beginning and end operands, j and k, are both unsigned, the increment operand i can be negative.

Data Types: fi |single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Ending operand, specified as a real scalar integer-valued fi object or built-in numeric type.

Data Types: fi |single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

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Fixed-Point Designer™ determines the data type of the y using the following rules:

  • The data type covers the union of the ranges of the fixed-point types of the input operands.

  • If either the beginning or ending operand is signed, the resulting data type is signed. Otherwise, the resulting data type is unsigned.

  • The word length of y is the smallest value such that the fraction length is 0 and the real-world value of the least-significant bit is 1.

  • If any of the operands is floating-point, the word length and signedness of y is derived from the fi operand.

  • If any of the operands is a scaled double, y is a scaled double.

  • The fimath of y is the same as the fimath of the input operands.

  • If all the fi objects are of data type double, the data type of y is double. If all the fi objects are of data type single, the data type of y is single. If there are both double and single inputs, and no fixed-point inputs, the output data type is single.

Version History

Introduced in R2013b

See Also

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