How to use Matlab's summation function sum

How to use Matlab's summation function sum: 1. Use the "S = sum(A)" method to sum; 2. Use the "S = sum(A,dim)" method to sum according to the specified dimension ;3. Use "S = sum(___,outtype)" to specify the data type of the output result.

The operating environment of this article: Windows 7 system, Matlab R2020a version, Dell G3 computer.

How to use Matlab’s summation function sum:

1. S = sum(A), summation

If x is a vector, calculate the sum of the elements of the vector, such as:

>> x = randi(10,1,10)
x =
     7     1     9    10     7     8     8     4     7     2
>> sum(x)
ans =
    63

If x is an array, calculate the sum of the columns of the array, such as:

>> x = pascal(4,2)
x =
    -1    -1    -1    -1
     3     2     1     0
    -3    -1     0     0
     1     0     0     0
>> sum(x)
ans =
     0     0     0    -1

2. S = sum(A,dim), sum according to the specified dimensions

dim = 1, means summing the columns

dim = 2, means summing the rows

dim = 3, means summing the pages

...., and so on

For example:

>> a = toeplitz(1:5)
a =
     1     2     3     4     5
     2     1     2     3     4
     3     2     1     2     3
     4     3     2     1     2
     5     4     3     2     1
>> sum(a,1)
ans =
    15    12    11    12    15
>> sum(a,2)
ans =
    15
    12
    11
    12
    15

3, S = sum (___,outtype) specifies the data type of the output result

The optional string parameters are 'double', 'default' and 'native'

Generally speaking, the default is ' default'

Sometimes we sum integers and want the result to be output as a double type, we can use this parameter

For example:

>> a = single(1:4)
a =
     1     2     3     4
>> class(sum(a,'double'))
ans =
double
>> class(sum(a))
ans =
single

Although the data types of Matlab are relatively Comprehensive, but data type conversion is not completely consistent with other languages, so you need to be careful when using it

4. Whether S = sum(___,nanflag) ignores NaN values

Sometimes when summing, there are NaN values ​​in the data, causing the calculation result to appear NaN. The general processing method is to use the isnan function to exclude nan values. With this option, it is simple

For example :

>> a = rand(1,6);a(randperm(6,2)) = NaN
a =
    0.7060    0.0318       NaN    0.0462    0.0971       NaN
>> sum(a)
ans =
   NaN
>> sum(a,'omitnan')
ans =
    0.8812

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