I have the following code written in Octave:
1 %-----------------------------------------------------------------------------%
2 % INPUT SIGNAL %
3 %-----------------------------------------------------------------------------%
4
5 sampling_frequency = 8000;
6 sampling_period = 1/sampling_frequency;
7 samples_count = 8;
8 time_samples = sampling_period * (0 : samples_count-1);
9
10
11 amplitude_1 = 1;
12 frequency_1 = 1000;
13 phase_shift_1 = 0;
14 signal_samples_1 = amplitude_1*sin(2*pi * frequency_1 * ...
15 time_samples + phase_shift_1);
16
17
18 amplitude_2 = 0.5;
19 frequency_2 = 2000;
20 phase_shift_2 = 3*pi/4;
21 signal_samples_2 = amplitude_2*sin(2*pi * frequency_2 * ...
22 time_samples + phase_shift_2);
23
24 signal_samples = signal_samples_1 + signal_samples_2;
25 for samples_index = 0 : samples_count-1
26 fprintf(stdout, "Sample %d: ", samples_index)
27 endfor
28
As you may see, at line 25, I would like to print value of each sample at separate line, i.e.
Sample <sample_number>: <sample_value>
My question is: how can I index separate member of an array (e.g. input_signal array)?
I have found the solution by myself, so I would like to share it with you.
signal_samples = signal_samples_1 + signal_samples_2;
for samples_index = 1 : samples_count
fprintf(stdout, "Sample %d: %8.5f\n", samples_index-1, ...
signal_samples(samples_index:samples_index))
endfor
Output:
Sample 0: 0.35355
Sample 1: 0.35355
Sample 2: 0.64645
Sample 3: 1.06066
Sample 4: 0.35355
Sample 5: -1.06066
Sample 6: -1.35355
Sample 7: -0.35355
Related
I am trying to resize a given image by sub-sampling it. I am using grayscae iamges.
The way I understand sub-sampling is basically this:
Let's say we have an 5x5 image and we want to resize it by a factor of 2, so the output image will be 3x3.
So if the 5x5 is: (1 2 3 4 5; 6 7 8 9 10; 11 12 13 14 15; 16 17 18 19 20; 21 22 23 24 25)
Then the 3x3 will be: (1 3 5; 11 13 15; 21 23 25)
So if the factor is 2, for the first row we take the first sample and then every second sample and so on. The same for columns.
The code that I wrote for this is:
i = 0;
j = 0;
for row=1:old_rows
if mod((row-1), a) == 0
i = i + 1;
end
for col=1:old_cols
if mod((row-1), a) == 0 && mod((col-1), a) == 0
j = j + 1;
sub_sampled_I(i, j) = I(row, col); % I is the input image
end
end
j = 0;
end
sub_sampled_I = im2uint8(sub_sampled_I);
end
The issue is that the final image has nothing to do with the original. It is just a white image with some black points here and there. What I understand wrong about sub-sampling?
Can any one help creating spiral matrix in matlab using only loops and if else conditions.
For example n=5, spiral matrix is:
17 16 15 14 13
18 5 4 3 12
19 6 1 2 11
20 7 8 9 10
21 22 23 24 25
There is a function spiral in your MATLAB installation, doing exactly what you want.
>> spiral(5)
ans =
21 22 23 24 25
20 7 8 9 10
19 6 1 2 11
18 5 4 3 12
17 16 15 14 13
You can view the source code typing edit spiral
Try this:
nn = input('');
n = floor(1+(nn)/2);
a = zeros(nn,nn);
i=n;j=n;m=1;br=true;
if rem(nn,2)==0
j=n-1;
nn=nn+2;
end
for p=1:2:nn
k=0;
while k<p-2
k=k+1;
a(i,j)=m;
i=i-1;
m=m+1;
end
k=0;
while k<p-1
k=k+1;
a(i,j)=m;
j=j-1;
m=m+1;
end
k=0;
while k<p-1
if j<1
br = false;
break
end
k=k+1;
a(i,j)=m;
i=i+1;
m=m+1;
end
if ~br
break
end
k=0;
while k<p
k=k+1;
a(i,j)=m;
j=j+1;
m=m+1;
end
end
disp(a)
Here is a sample run:
Enter the number:
5
17 16 15 14 13
18 5 4 3 12
19 6 1 2 11
20 7 8 9 10
21 22 23 24 25
Another one, this time using an even number:
Enter the number:
6
36 35 34 33 32 31
17 16 15 14 13 30
18 5 4 3 12 29
19 6 1 2 11 28
20 7 8 9 10 27
21 22 23 24 25 26
Explanation: It starts with the central cell in the case of an odd number as input, and the bottom-left central cell in the case of an even input. It then, starting with 1 as the value and taking one circulation at a time, moves outwards, traverses right, up, left, down, and right again, incrementing the value to be assigned with each step, until the entire matrix is full.
Here is a custom function SpiralMatrix to construct the spiral matrix as your requested
function M = SpiralMatrix(n)
M = zeros(n);
% start from element M(1,1)
i = 1;
j = 1;
s = 1; % first element assigned to M(1,1)
M(i,j) = s;
while true
% fill row from left to right
idx = find(M(i,:)==0,1,'last');
M(i,j:idx) = s + (0:(idx-j));
s = s + idx - j;
j = idx;
% fill column from top to bottom
idx = find(M(:,j)==0,1,'last');
M(i:idx,j) = s + (0:(idx-i));
s = s + idx - i;
i = idx;
% fill row from right to left
idx = find(M(i,:)==0,1,'first');
M(i,j:-1:idx) = s + (0:(j-idx));
s = s + j - idx;
j = idx;
% fill column from bottom to top
idx = find(M(:,j)==0,1,'first');
M(i:-1:idx,j) = s + (0:(i-idx));
s = s + i-idx;
i = idx;
% break if matrix if fully filled
if nnz(M) == n^2
break;
end
end
M = n^2+1-fliplr(flipud(M));
end
such that
>> SpiralMatrix(5)
ans =
17 16 15 14 13
18 5 4 3 12
19 6 1 2 11
20 7 8 9 10
21 22 23 24 25
>> SpiralMatrix(7)
ans =
37 36 35 34 33 32 31
38 17 16 15 14 13 30
39 18 5 4 3 12 29
40 19 6 1 2 11 28
41 20 7 8 9 10 27
42 21 22 23 24 25 26
43 44 45 46 47 48 49
I have 2 inner while loops. Code writes the results to first row on the matrix but when it gets to second row, it just passes the other rows and doesn't fill the columns of the rows. How to solve it? The code and output are like below:
while i <= m-1
i
while a <= m-1
a
den1 = sqrt(((xy{i,j}-xy{a+1,b})^2+(xy{i,j+1}-xy{a+1,b+1})^2 ));
dMat(i,a) = den1;
a = a+1;
end
i = i+1;
end
i = 1
a = 1
a = 2
a = 3
a = 4
a = 5
a = 6
a = 7
a = 8
a = 9
a = 10
a = 11
a = 12
a = 13
a = 14
a = 15
a = 16
a = 17
a = 18
a = 19
a = 20
a = 21
a = 22
a = 23
a = 24
i = 2
i = 3
i = 4
i = 5
i = 6
i = 7
i = 8
i = 9
i = 10
i = 11
i = 12
i = 13
i = 14
i = 15
i = 16
i = 17
i = 18
i = 19
i = 20
i = 21
i = 22
i = 23
i = 24
You have to restart a to a=1 for each iteration. Put it above the while a <= m-1
x=[3 1 1 -5 -2 0 1 2 -2 2];
A=[4 2 6; 0 1 -3; -2 5 -2];
B=[-2 3 2; 1 5 5; -3 1 0];
sum=0;
for i=2:3
sum_j=0;
for j=1:2
sum_j=sum_j+A(1,j)*B(j,i);
end
sum=sum+A(2,i)*sum_j;
end
fprintf('(c) %g\n',sum);
>> (c) -32
-32 is a correct answer. However, if I initialize sum_j=0 outside of the the loop, it returns a different value.
sum=0;
sum_j=0;
for i=2:3
for j=1:2
sum_j=sum_j+A(1,j)*B(j,i);
end
sum=sum+A(2,i)*sum_j;
end
fprintf('(c) %g\n',sum);
>> (c) -98
Can anyone explain why this is happening?
In your first code sum_j gets reinitialized in the loop for i and in second code sum_j carry the value in each loop. Here is a simulation of your codes
first code:
sum = 0
i=2:
sum_j = 0
i=2,j=1
sum_j = 0 + 4*3 = 12
i=2,j=2
sum_j = 12 + 2*5 = 22
sum = 0 + 1*22 = 22
i=3
sum_j = 0
i=3,j=1
sum_j = 0 + 4*2 = 8
i=3,j=2
sum_j = 8 + 2*5 = 18
sum = 22 + -3*18 = -32
Second code
sum = 0
sum_j = 0
i=2:
i=2,j=1
sum_j = 0 + 4*3 = 12
i=2,j=2
sum_j = 12 + 2*5 = 22
sum = 0 + 1*22 = 22
i=3
i=3,j=1
sum_j = 22 + 4*2 = 30
i=3,j=2
sum_j = 30 + 2*5 = 40
sum = 22 + -3*40 = -98
I am given a number N, and i must add some numbers from the array V so that they wil be equal. V is consisting of numbers that are all powers of 3:
N = 17
S = 0
V = 1 3 9 27 81 ..
I should add numbers from V to N and S in order to make them equal. The solution to the example above is :
17 + 1 + 9 = 27, 27, 1 and 9 are taken from V, a number from V can be taken only once, and when taken it's removed from V.
I tried sorting V and then adding the biggest numbers from V to S until S has reached N, but it fails on some tests when it's like:
N = 7
S = 0
V = 1 3 9 27
So the solution will be:
7 + 3 = 9 + 1
In examples like this i need to add numbers both to N and S, and also select them so they become equal.
Any idea of solving this ? Thanks.
Write N in base 3: 17 = 2*1 + 2*3 + 1*9
Find the first power of 3 with coefficient 2, in this case 1.
Add this power of 3: 17 + 1
Repeat until all coefficients are 0 or 1.
17 = 2*1 + 2*3 + 1*9
17 + 1 = 2*9
17 + 1 + 9 = 27
7 = 1*1 + 2*3
7 + 3 = 1*1 + 1*9