I wrote a code in Matlab which I predefine the variable "a" and then set up a for loop of 5 iterations where the variable "a" goes through some basic operations. However, the for loop output only saves the fifth iteration of "a." How do I save all 5 iterations in a 1x5 array?
The code is as follows:
a = 10;
k = 0.5;
n = 2;
for m = 1:5
a = a + (a*k) + n;
end
Edit:
I just found it that I have to create a new variable.
a = 10;
k = 0.5;
n = 2;
a_n = zeros(1,5);
for m = 1:5
a = a + (a*k) + n;
a_n(m) = a;
end
You may need to store value of a after each iteration into an another variable x
a = 10;
k = 0.5;
n = 2;
for m = 1:5
a = a + (a*k) + n;
x(m) = a;
end
x
Output:
x =
17.000 27.500 43.250 66.875 102.312
You would need to use a different variable to store the 5 iterations as an array.
Code would look something like this:
a = 10;
k = 0.5;
n = 2;
b = [];
for m = 1:5
a = (a + (a*k) + n)
b = [b a];
end
You can now print b for all 5 iteration values.
Here is an alternate way to update values into the 1-D matrix.
Related
I am trying to implement the following loop inside of matlab
The difficulty I am having is implementing the sum sign such that I get the correct values. The first row of my X matrix is correct but the second row is not and I cant figure out why.
J = [200 100 300];
k = [3e6 2e6 4e6];
n = 3;
points = 300;
for j = 1:points
w(j)=j;
end
x = zeros(n+1,points);
x(1,:)=1;
for j = 1:points
sumJx = 0;
for i = 2:n+1
sumJx = sum(J(1:i-1)*x(1:i-1,j));
x(i,j) = x(i-1) - (w(j)^2 / k(i-1)) * sumJx;
end
end
f_omega = x(n+1,:);
plot(w,f_omega);
ylim([-40 3])
I would like to write a Matlab code to calculate the following:
\sum_{k=0}^{N-1} \frac{1}{k!} \sum_{i=0}^{k} {k \choose i}(a-1)^{k-i} a^k
and my code is:
N = 3;
a = [3 4];
for k = 0:N-1
f = 0;
for i = 0:k
f = f + nchoosek(k,i).* a.^k .* (a-1).^(k-i);
end
sumoff = sum(f);
all = (( 1./ (factorial(k))).*sumoff);
end
overall= sum(all);
'all' variable gives different value when it is inside the for loop rather than outside. But I want it to calculate when k = 0:N-1. What am I doing wrong?
Thank you.
The issue is your current code overwrites all on every iteration. Moving it outside the loop also doesn't work because you'll only save the result of the last iteration.
To save the all of every iteration, define all as a vector and then assign each intermediate result into that vector:
N = 3;
a = [3 4];
% preallocate a vector for `all`
all = nan(N-1, 1);
for k = 0:N-1
f = 0;
for i = 0:k
f = f + nchoosek(k,i) .* a.^k .* (a-1).^(k-i);
end
sumoff = sum(f);
% assign your intermediate result into the `all` vector
all(k+1) = ((1./(factorial(k))) .* sumoff);
end
overall = sum(all);
I want the function P to look like this:
-1 + 0.6366*(x+pi/2) + (-0.000)*(x + pi/2)*(x)
and right now it looks like this
(5734161139222659*x)/9007199254740992 + (5734161139222659*pi)/18014398509481984 - (8131029572207409*x*(x + pi/2))/324518553658426726783156020576256 - 1.
How to convert S array so that the values are not symbolic?
syms P x
f = sin(x);
f = matlabFunction(f);
X = [-pi/2, 0, pi/2];
Y = f(sym(X));
P = MetN(X,Y,x)
P = matlabFunction(P);
function [P] = MetN(X,Y,x)
n = length(X);
for i = 1:n
A(i,1) = 1;
end
for i = 2:n
for j = 2: n
if i >= j
produs = 1;
for k =1:j-1
produs = produs * (X(i) - X(k));
end
A(i,j) = produs;
end
end
end
S = SubsAsc(A, Y);
S = double(S);
disp(S);
sym produs
P = double(sym(S(1)));
for i = 2:n
produs = 1;
for j = 1:i-1
produs = produs * (x - sym(X(j)));
end
disp(produs);
P = P + double(S(i))*produs;
end
end
function [x] = SubsAsc(A,b)
n = length(b);
x(1) = (1/A(1,1))*b(1);
for k = 2:n
s = 0;
for j = 1:k-1
s = s + A(k,j)*x(j);
end
x(k) = (1/A(k,k))*(b(k)-s);
end
end
The output you currently have is because symbolic uses exact arithmetic, so it outputs it as a rational number (hence the ugly fraction).
To have it output P using decimals, use vpa(). For instance output P using decimals to 5 significant digits
>> vpa(P, 5)
ans =
0.63662*x - 2.5056e-17*x*(x + 1.5708)
This will, however, also round pi, so you can't really have the best of both worlds here.
I'm trying to write my own program to sort vectors in matlab. I know you can use the sort(A) on a vector, but I'm trying to code this on my own. My goal is to also sort it in the fewest amount of swaps which is kept track of by the ctr variable. I find and sort the min and max elements first, and then have a loop that looks at the ii minimum vector value and swaps it accordingly.
This is where I start to run into problems, I'm trying to remove all the ii minimum values from my starting vector but I'm not sure how to use the ~= on a vector. Is there a way do this this with a loop? Thanks!
clc;
a = [8 9 13 3 2 8 74 3 1] %random vector, will be function a once I get this to work
[one, len] = size(a);
[mx, posmx] = max(a);
ctr = 0; %counter set to zero to start
%setting min and max at first and last elements
if a(1,len) ~= mx
b = mx;
c = a(1,len);
a(1,len) = b;
a(1,posmx) = c;
ctr = ctr + 1;
end
[mn, posmn] = min(a);
if a(1,1) ~= mn
b = mn;
c = a(1,1);
a(1,1) = b;
a(1,posmn) = c;
ctr = ctr + 1;
end
ii = 2; %starting at 2 since first element already sorted
mini = [mn];
posmini = [];
while a(1,ii) < mx
[mini(ii), posmini(ii - 1)] = min(a(a~=mini))
if a(1,ii) ~= mini(ii)
b = mini(ii)
c = a(1,ii)
a(1,ii) = b
a(1,ii) = c
ctr = ctr + 1;
end
ii = ii + 1;
end
I am currently trying to run a script that calls a particular function, but want to call the function inside a loop that halfs one of the input variables for roughly 4 iterations.
in the code below the function has been replaced for another for loop and the inputs stated above.
the for loop is running an Euler method on the function, and works fine, its just trying to run it with the repeated smaller step size im having trouble with.
any help is welcomed.
f = '3*exp(-x)-0.4*y';
xa = 0;
xb = 3;
ya = 5;
n = 2;
h=(xb-xa)/n;
x = xa:h:xb;
% h = zeros(1,4);
y = zeros(1,length(x));
F = inline(f);
y(1) = ya;
for j = 1:4
hOld = h;
hNew = hOld*0.5;
hOld = subs(y(1),'h',hNew);
for i = 1:(length(x)-1)
k1 = F(x(i),y(i));
y(i+1,j+1) = y(i) + h*k1;
end
end
disp(h)
after your comment, something like this
for j = 1:4
h=h/2;
x = xa:h:xb;
y = zeros(1,length(x));
y(1) = ya;
for i = 1:(length(x)-1)
k1 = F(x(i),y(i));
y(i+1,j+1) = y(i) + h*k1;
end
end