# how to get only row position of data?

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how to get only row position of data in a matrix and store in other array

Mar 20th, 2018

MATLAB is an abbreviation for "matrix laboratory." While other programming languages mostly work with numbers one at a time, MATLAB®is designed to operate primarily on whole matrices and arrays.

All MATLAB variables are multidimensional arrays, no matter what type of data. A matrix is a two-dimensional array often used for linear algebra.

### Array Creation

To create an array with four elements in a single row, separate the elements with either a comma (,) or a space.

`a = [1 2 3 4]`

returns

```a =

1     2     3     4```

This type of array is a row vector.

To create a matrix that has multiple rows, separate the rows with semicolons.

`a = [1 2 3; 4 5 6; 7 8 10]`
```a =

1     2     3
4     5     6
7     8    10```

Another way to create a matrix is to use a function, such as ones, zeros, or rand. For example, create a 5-by-1 column vector of zeros.

`z = zeros(5,1)`
```z =

0
0
0
0
0```

### Matrix and Array Operations

MATLAB allows you to process all of the values in a matrix using a single arithmetic operator or function.

`a + 10`
```ans =

11    12    13
14    15    16
17    18    20```
`sin(a)`
```ans =

0.8415    0.9093    0.1411
-0.7568   -0.9589   -0.2794
0.6570    0.9894   -0.5440```

To transpose a matrix, use a single quote ('):

`a'`
```ans =

1     4     7
2     5     8
3     6    10```

You can perform standard matrix multiplication, which computes the inner products between rows and columns, using the * operator. For example, confirm that a matrix times its inverse returns the identity matrix:

`p = a*inv(a)`
```p =

1.0000         0   -0.0000
0    1.0000         0
0         0    1.0000```

Notice that p is not a matrix of integer values. MATLAB stores numbers as floating-point values, and arithmetic operations are sensitive to small differences between the actual value and its floating-point representation. You can display more decimal digits using the formatcommand:

```format long
p = a*inv(a)```
```p =

1.000000000000000                   0  -0.000000000000000
0   1.000000000000000                   0
0                   0   0.999999999999998```

Reset the display to the shorter format using

`format short`

format affects only the display of numbers, not the way MATLAB computes or saves them.

To perform element-wise multiplication rather than matrix multiplication, use the .* operator:

`p = a.*a`
```p =

1     4     9
16    25    36
49    64   100```

The matrix operators for multiplication, division, and power each have a corresponding array operator that operates element-wise. For example, raise each element of a to the third power:

`a.^3`
```ans =

1           8          27
64         125         216
343         512        1000```

### Concatenation

Concatenation is the process of joining arrays to make larger ones. In fact, you made your first array by concatenating its individual elements. The pair of square brackets [] is the concatenation operator.

`A = [a,a]`
```A =

1     2     3     1     2     3
4     5     6     4     5     6
7     8    10     7     8    10```

Concatenating arrays next to one another using commas is called horizontal concatenation. Each array must have the same number of rows. Similarly, when the arrays have the same number of columns, you can concatenate vertically using semicolons.

`A = [a; a]`
```A =

1     2     3
4     5     6
7     8    10
1     2     3
4     5     6
7     8    10```

### Complex Numbers

Complex numbers have both real and imaginary parts, where the imaginary unit is the square root of –1.

`sqrt(-1)`
```ans =

0 + 1.0000i```

To represent the imaginary part of complex numbers, use either i or j.

`c = [3+4i, 4+3j, -i, 10j]`
```c =

3.0000 + 4.0000i   4.0000 + 3.0000i   0 - 1.0000i   0 +10.0000i```

Jun 18th, 2013

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Mar 20th, 2018
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Mar 20th, 2018
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