I am doing some simulations studies and for initial stuides I am trying to simulate 100 gas particles and then grouping of these gas particles in 5 groups randomly for 10 or 100 times (non zero values in any groups). after that i have to find the group with highest particle and the number.
for example
100 gas particles
1 2 3 4 5(groups) Total particle group/Highest number
20|20|20|20|20 100 1-2-3-4-5/20
70|16|04|01|09 100 1/70
18|28|29|10|15 100 3/29
.
.
etc
i have used this to generate 5 random numbers for a single time
for i=1:1
randi([1,100],1,5)
end
ans =
50 41 9 60 88
but how will i find the highest number and group?
Use the max function :
a = [50 41 9 60 88];
[C,I] = max(a)
C should be equal to 88 and I to 4.
For the special case of equality (first line in your code), you have to read the documentation to see the result of max. I think the index returned will be the first max.
Related
I have an array (2000x2) with two variables and want to calculate the mean of column 2 at intervals determined by column 1. How can i do this?
speed=(:,1); %values range from 0-100 cm/s
press=(:,2);
I want to calculate mean pressure at at 5 cm/s intervals of speed. So that I get 20 values for pressure that correspond to 20 intervals of speed.
Should be simple, but I'm still a beginner in Matlab.
The accumarray function does just that:
data = [0 20 33 44 22 56 25 47 81 90; 3 5 4 3 2 4 5 5 6 0].';
speed = data(:,1);
press = data(:,2);
sz = 5; % interval size
fill = NaN; % fill value in the result, for empty groups
group = floor(speed/sz)+1; % compute index of group for each value
result = accumarray(group, press, [], #mean, NaN); % compute mean of each group
If I have two lists:
a:1 2 3 4;
b:10 20 30 40;
I want to sum the product of the two lists within a window of 2. So the result set should be:
10 50 130 250
For example, to get the result of 130 it would be (2*20)+(3*30) = 130
sums 2 mavg '(a*b)
seems to get me part way there, but the window of 2 isn't being applied. I've tried experimenting with sum, sums, sum each, wavg, mavg, etc. and I am completely stuck. Could anyone help? Thanks!
This line should work for you:
2 msum a*b
as demonstrated here:
q)a:1 2 3 4
q)b:10 20 30 40
q)2 msum a*b
10 50 130 250
For more information about the keyword msum, you could check out the Kx Reference page:
https://code.kx.com/wiki/Reference/msum
Hope that helps!
Alternatively you could use the adverb each prior:
q)+':[a*b]
However this will only work with a window size of 2 and if your data contains null values this needs to be padded with 0:
q)+':[0^a*b2]
On a positive note it is faster than using msum in this situation.
q)\ts:1000000 +':[0^a*b2]
940 1264
q)\ts:1000000 2 msum a*b2
1556 1104
I have two set of numbers and want to compare and rank them relative to each other in MATLAB.
The data is:
x = [3 7 8 25 33 52 64 65 78 79 91 93];
y = [7 10 12 27 30 33 57 62 80 83 85 90];
I started with the for/if/else commands and got stuck in the middle.
In other words, I want to get the answer through MATLAB how many times the numbers in the first group (x) are bigger than the ones in the second group (y).
I got started with sorting etc.
n1 = length(data1);
n2 = length(data2);
xs = sort(x);
ys = sort(y);
r1 = zeros(1,n1);
r2 = zeros(1,n2);
I am open to use other commands than this kind of sorting and for/if/else, it doesn't really matter, just need some help in the right direction.
I am not entirely sure I understand what you're trying to do there. Is it safe to assume that the two vectors will be of the same size?
You could simply do an element wise division of the 2 sorted vectors and get the statistics from there.
For example:
div = xs./ys;
max_div = max(div)
mean_div = mean(div)
This is equivalent to running a for loop and dividing each element in the xs array by each element in the ys array for that corresponding index. The 'max' and 'mean' are obviously the largest quotient and the mean quotient.
In MATLAB, to find how many times each of the numbers in vector x are bigger than numbers in vector y:
sum(x > y.')
This uses the transpose of y to create a size(x) by size(y) matrix with a 1 when a number in x is greater than a number in y, then sums each column.
For your data, the result is the following vector, with an item for each number in x:
[0 0 1 3 5 6 8 8 8 8 12 12]
The vectors x and y don't have to be sorted. If you need the total number of times, just apply sum again to the result.
I want to calculate the sum of the elements surrounding a given element in a matrix. So far, I have written these lines of code:
for i=1:m,
rij(1:n)=0
for j=1:n,
alive = tijdelijk(i-1,j)+tijdelijk(i+1,j)+tijdelijk(i-1,j-1)+tijdelijk(i+1,j-1)+tijdelijk(i,j+1)+tijdelijk(i,j-1)+tijdelijk(i-1,j+1)+tijdelijk(i+1,j+1)
This results in an error because, for example, i-1 becomes zero for i=1. Anyone got an idea how to do this without getting this error?
You can sum the elements via filtering. conv2 can be used for this manner.
Let me give an example. I create a sample matrix
>> A = reshape(1:20, 4, 5)
A =
1 5 9 13 17
2 6 10 14 18
3 7 11 15 19
4 8 12 16 20
Then, I create a filter. The filter is like a mask where you put the center on the current cell and the locations corresponding to the 1's on the filter are summed. For eight-connected neighbor case, the filter should be as follows:
>> B = [1 1 1; 1 0 1; 1 1 1]
B =
1 1 1
1 0 1
1 1 1
Then, you simply convolve the matrix with this small matrix.
>> conv2(A, B, 'same')
ans =
13 28 48 68 45
22 48 80 112 78
27 56 88 120 83
18 37 57 77 50
If you want four-connected neighbors, you can make the corners of your filter 0. Similarly, you can design any filter for your purpose, such as for averaging all neighbors instead of summing them.
For details, please see the convolution article in Wikipedia.
Two possibilities : change the limits of the loops to i=k:(m-k) and j=k:(n-k) or use blkproc
ex :
compute the 2-D DCT of each 8-by-8 block
I = imread('cameraman.tif');
fun = #dct2;
J = blkproc(I,[8 8],fun);
imagesc(J), colormap(hot)
There are lots of things you can do at the edges. Which you do depends very specifically on your problem and is different from usage case to usage case. Typical things to do:
If (i-1) or (i+1) is out of range, then just ignore that element. This is equivalent to zero padding the matrix with zeros around the outside and adjusting the loop limits accordingly
Wrap around the edges. In other words, for an MxN matrix, if (i-1) takes you to 0 then instead of taking element (i-1, j) = (0, j) you take element (M, j).
Since your code mentions "your teacher" I'd guess that you can ask what should happen at the edges (or working it out in a sensible manner may well be part of the task!!).
I have an m x n matrix and I want to use it in some neural networks applications in MATLAB.
For example,
A = [ 24 22 35 40 30 ; 32 42 47 45 39 ; 14 1 10 5 9 ; 2 8 4 1 8] ;
I want to randomly train some columns and test the other remaining columns.
So, the first matrix will contain three random, distinct columns taken from the original matrix A, while the second matrix contains the remaining two columns.
How can I extract these matrices ?
This will do:
s = randperm(5);
train = A(:, s(1:3));
test = A(:, s(4:end));
Neural Network Toolbox comes with a set of functions that do this for you, such as dividerand and divideblock.