I am trying to write a simple MATLAB program that will find the first chain (more than 70) of consecutive nonzero values and return the starting value of that consecutive chain.
I am working with movement data from a joystick and there are a few thousand rows of data with a mix of zeros and nonzero values before the actual trial begins (coming from subjects slightly moving the joystick before the trial actually started).
I need to get rid of these rows before I can start analyzing the movement from the trials.
I am sure this is a relatively simple thing to do so I was hoping someone could offer insight.
Thank you in advance
EDIT: Here's what I tried:
s = zeros(size(x1));
for i=2:length(x1)
if(x1(i-1) ~= 0)
s(i) = 1 + s(i-1);
end
end
display(S);
for a vector x1 which has a max chain of 72 but I dont know how to find the max chain and return its first value, so I know where to trim. I also really don't think this is the best strategy, since the max chain in my data will be tens of thousands of values.
This answer is generic for any chain size. It finds the longest chain in a vector x1 and retrieves the first element of that chain val.
First we'll use bwlabel to label connected components, For example:
s=bwlabel(x1);
Then we can use tabulate to get a frequency table of s, and find the first element of the biggest connected component:
t=tabulate(s);
[C,I]=max(t(:,2));
val=x1(find(s==t(I,1),1, 'first'));
This should work for the case you have one distinct maximal size chain. What happens for the case if you have more than one chain that has maximal lengths? (you can still use my code with slight modifications...)
You don't need to use an auxiliary vector to keep track of the index:
for i = 1:length(x)
if x(i) ~= 0
count = count + 1;
elseif count >= 70
lastIndex = i;
break;
else
count = 0;
end
if count == 70
index = i - 69;
end
end
To remove all of the elements in the chain from x, you can simply do:
x = x([lastIndex + 1:end]);
EDIT (based off comment):
The reason that the way you did it didn't work was because you didn't reset the counter when you ran into a 0, that's what the:
else
count = 0;
is for; it resets the process, if you will.
For some more clarity, in your original code, this would be reflected by:
if x1(i-1) ~= 0
s(i) = 1 + s(i-1);
else
s(i) = 0;
end
Related
I have a scatter plot of approximately 30,000 pts, all of which lie above a horizontal line which I've visually defined in my plot. My goal now is to sum the vertical distance of all of these points to this horizontal line.
The data was read in from a .csv file and is already saved to the workspace, but I also need to check whether a value is NaN, and ignore these.
This is where I'm at right now:
vert_deviation = 0;
idx = 1;
while idx <= numel(my_data(:,5)) && isnan(idx) == 0
vert_deviation = vert_deviation + ((my_data(idx,5) - horiz_line_y_val));
idx = idx + 1;
end
I know that a prerequisite of using the && operator is having two logical statements I believe, but I'm not sure how to rewrite this loop in this way at the moment. I also don't understant why vert_deviation returns NaN at the moment, but I assume this might have to do with the first mistake I described...
I would really appreciate some guidance here - thank you in advance!
EDIT: The 'horizontal line' is a slight oversimplification - in reality the lower limit I need to find the distance to consists of 6 different line segments
I should have specified that the lower limit to which I need to calculate the distance for all scatterplot points varies for different x values (the horizontal line snippet was meant to be a simplification but may have been misleading... apologies for that)
I first modified the data I had already read into the workspace by replacing all NaNvalues with 0. Next, I wrote a while loop which defines the number if indexes to loop through, and defined an && condition to filter out any zeroes. I then wrote a nested if loop which checks what range of x values the given index falls into, and subsequently takes the delta between the y values of a linear line lower limit for that section of the plot and the given point. I repeated this for all points.
while idx <= numel(my_data(:,3)) && not(my_data(idx,3) == 0)
...
if my_data(idx,3) < upper_x_lim && my_data(idx,5) > lower_x_lim
vert_deviation = vert_deviation + (my_data(idx,4) - (m6 * (my_data(idx,5)) + b6))
end
...
m6 and b6 in this case are the slope and y intercept calculated for one section of the plot. The if loop is repeated six times for each section of the lower limit.
I'm sure there are more elegant ways to do this, so I'm open to any feedback if there's room for improvement!
Your loop doesn't exclude NaN values becuase isnan(idx) == 0 checks to see if the index is NaN, rather than checking if the data point is NaN. Instead, check for isnan(my_data(idx,5)).
Also, you can simplify your code using for instead of while:
vert_deviation = 0;
for idx=1:size(my_data,1)
if !isnan(my_data(idx,5))
vert_deviation = vert_deviation + ((my_data(idx,5) - horiz_line_y_val));
end
end
As #Adriaan suggested, you can remove the loop altogether, but it seems that the code in the OP is an oversimplification of the problem. Looking at the additional code posted, I guess it is still possible to remove the loops, but I'm not certain it will be a significant speed improvement. Just use a loop.
I am trying to write a MATLAB function that accepts non-integer, n, and then returns the factorial of it, n!. I am supposed to use a for loop. I tried with
"for n >= 0"
but this did not work. Is there a way how I can fix this?
I wrote this code over here but this doesn't give me the correct answer..
function fact = fac(n);
for fact = n
if n >=0
factorial(n)
disp(n)
elseif n < 0
disp('Cannot take negative integers')
break
end
end
Any kind of help will be highly appreciated.
You need to read the docs and I would highly recommend doing a basic tutorial. The docs state
for index = values
statements
end
So your first idea of for n >= 0 is completely wrong because a for doesn't allow for the >. That would be the way you would write a while loop.
Your next idea of for fact = n does fit the pattern of for index = values, however, your values is a single number, n, and so this loop will only have one single iteration which is obviously not what you want.
If you wanted to loop from 1 to n you need to create a vector, (i.e. the values from the docs) that contains all the numbers from 1 to n. In MATLAB you can do this easily like this: values = 1:n. Now you can call for fact = values and you will iterate all the way from 1 to n. However, it is very strange practice to use this intermediary variable values, I was just using it to illustrate what the docs are talking about. The correct standard syntax is
for fact = 1:n
Now, for a factorial (although technically you'll get the same thing), it is clearer to actually loop from n down to 1. So we can do that by declaring a step size of -1:
for fact = n:-1:1
So now we can find the factorial like so:
function output = fac(n)
output = n;
for iter = n-1:-1:2 %// note there is really no need to go to 1 since multiplying by 1 doesn't change the value. Also start at n-1 since we initialized output to be n already
output = output*iter;
end
end
Calling the builtin factorial function inside your own function really defeats the purpose of this exercise. Lastly I see that you have added a little error check to make sure you don't get negative numbers, that is good however the check should not be inside the loop!
function output = fac(n)
if n < 0
error('Input n must be greater than zero'); %// I use error rather than disp here as it gives clearer feedback to the user
else if n == 0
output = 1; %// by definition
else
output = n;
for iter = n-1:-1:2
output = output*iter;
end
end
end
I don't get the point, what you are trying to do with "for". What I think, what you want to do is:
function fact = fac(n);
if n >= 0
n = floor(n);
fact = factorial(n);
disp(fact)
elseif n < 0
disp('Cannot take negative integers')
return
end
end
Depending on your preferences you can replace floor(round towards minus infinity) by round(round towards nearest integer) or ceil(round towards plus infinity). Any round operation is necessary to ensure n is an integer.
I've run an experiment where a machine exerts a force on a bridge until it breaks. I need to cycle through my entire data set and calculate the toughness until I've hit the breaking point (fdValue1).
The toughness is calculated by summing up all the rectangles under my load vs. distance curve. (Basically the integral)
However, I have not been able to find a reasonable way of doing so and my current loop is an infinite loop and I'm not sure why.
%Initializing variables
bridge1Data = xlsread('Bridge1Data.xlsx', 'A2:C2971');
bridge2Data = xlsread('Bridge2Data.xlsx', 'A2:C1440');
bridge1Load = bridge1Data(:, 2);
bridge2Load = bridge2Data(:, 2);
bridge1Dist = bridge1Data(:, 3);
bridge2Dist = bridge2Data(:, 3);
[row1, col1] = size(bridge1Dist);
[row2, col2] = size(bridge2Dist);
bridge1Disp = zeros(row1, col1);
bridge2Disp = zeros(row2, col2);
fdValue1 = 0.000407350000000029;
&Main code
%Displacement
for k = 2:length(bridge1Dist)
bridge1Disp(k-1, 1) = bridge1Dist(k, 1) - bridge1Dist(k-1, 1);
end
%Max Load Bridge 1
maxLoad1 = 0;
for n = 1:length(bridge1Load)
for k = 1
if bridge1Load(n, k) > maxLoad1
maxLoad1 = bridge1Load(n, k);
end
end
end
%Cycle through data till failure, change proj data
totalRect1 = 0;
for j = 2:length(bridge1Disp)
while bridge1Disp(j, 1) ~= fdValue1
rectangle = (bridge1Disp(j, 1) - bridge1Disp(j-1, 1))*...
((bridge1Load(j, 1) + bridge1Load(j-1, 1))/2);
totalRect1 = totalRect1 + rectangle;
end
end
Basically, I make an array for the load and distance the machine pushes down on the bridge, assign a 'Failure Distance' value (fdValue) which should be used to determine when we stop calculating toughness. I then calculate displacement, calculate the maximum load. Then through the variable 'rectangle', calculate each rectangle and sum them all up in 'totalRect1', and use that to calculate the toughness by finding the area under the curve. Is anyone able to see why the loop is an infinite loop?
Thanks
The problem with the condition while bridge1Disp(j, 1) ~= fdValue1 is that you need to check for <= and not for (in)equality, since double numbers will almost never evaluate to be equal even if they seem so. To read more about this you can look here and also google for matlab double comparison. Generally it has something to do with precision issues.
Usually when checking for double equality you should use something like if abs(val-TARGET)<1E-4, and specify some tolerance which you are willing to permit.
Regardless,
You don't need to use loops for what you're trying to do. I'm guessing this comes from some C-programming habits, which are not required in MATLAB.
The 1st loop (Displacement), which computes the difference between every two adjacent elements can be replaced by the function diff like so:
bridge1Disp = diff(bridge1Dist);
The 2nd loop construct (Max Load Bridge 1), which retrieves the maximum element of bridge1Load can be replaced by the command max as follows:
maxLoad1 = max(bridge1Load);
For the last loop construct (Cycle ...) consider the functions I've mentioned above, and also find.
In the code section
%Cycle through data till failure, change proj data
totalRect1 = 0;
for j = 2:length(bridge1Disp)
while bridge1Disp(j, 1) ~= fdValue1
rectangle = (bridge1Disp(j, 1) - bridge1Disp(j-1, 1))*...
((bridge1Load(j, 1) + bridge1Load(j-1, 1))/2);
totalRect1 = totalRect1 + rectangle;
end
end
the test condition of the while loop is
bridge1Disp(j, 1) ~= fdValue1
nevertheless, in the while loop the value of bridge1Disp(j, 1) does not change so if at the first iteratiion of the while loop bridge1Disp(j, 1) is ~= fdValue1 the loop will never end.
Hope this helps.
I need to write a recursive function embedded with quicksort algorithm.
I'm having trouble when updating the new boundaries. y is a matrix and m is the num of the row needs to be sorted.Please help...
function [y]=quicksort(y,left,right,m)
i=left;
j=right;
num=randi(length(y)); % pick a random element in the array as pivot
pivot=y(m,num);
if i <= j %find the element fits criteria below before i overlaps j.
while y(m,i) < pivot
i = i + 1;
end
while y(m,j) > pivot
j = j - 1;
end
ytmp=y(:,j);
y(:,j)=y(:,i);
y(:,i)=ytmp;
i = i + 1;
j = j - 1;
%swap the positions of the two elements when y(m,j) < pivot < y(m,i)
else
return
end
return
[y]=quicksort(y,i,right,m); %update the boundaries.
[y]=quicksort(y,left,j,m); %recursively call the function.
You have done some errors. However, since this seems to be homework I will give you some concrete hints and examples instead of posting the right answer directly. I also limit this to a single vector to keep the answer simpler and more concise.
First, you want to swap all elements which are on the wrong side of the pivot element, not only the first element. So the tip is to use a while loop. You will however still need to do the swapping somewhere, so you will need an if-statement somewhere as well. Secondly, the last return will always be executed. This means that you will never enter the recursion. Try to instead use a condition where you only continue iterating in case the number of elements left exeeds one.
if (i < right)
y=qsort(y,i,right); %update the boundaries.
end
if (left < j)
y=qsort(y,left,j); %recursively call the function.
end
Hope this information is enough. Good luck!
I'm trying to code my own implementation of Linear Feedback Shift Register on Matlab in order to generate a pseudo-random sequence of numbers. Suppose I need to generate a sequence from 1 to 16,384 (2^14) in random order, my initial state is number 329 and the tap is 7.
This is the code I've got so far:
function [rndV] = lfsr(limit, init, tap)
X = -1;
rndV = init;
bits = nextpow2(limit);
while(X ~= init)
if(X == -1)
X = init;
end
a = bitget(X, bits);
b = bitget(X, tap);
X = bitshift(X,1,bits);
X = bitset(X,1,bitxor(a,b));
rndV = [rndV X];
end
end
The parameters are:
limit = 16,384
init = 329
tap = 7
If I get right LFSR, must the algorithm loop until the initial state is found again? Does this loop must generate all numbers between 1 and 16,384 in random order?
Something is wrong on my code or maybe I misunderstood LFSR algorithm, but I'm getting just 22 numbers in random order, then the initial state (329) is found again.
I want to achieve the same as described here but in matlab.Thanks!
only a primitive polynomial can got full range of random numbers. check here for primpolyes, or here if you need bigger order of LSFR