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# Roger Stafford

2,138 total contributions since 2008

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Answered
How to plot an Ellipse
Let (x1,y1) and (x2,y2) be the coordinates of the two vertices of the ellipse's major axis, and let e be its eccentricity. a =...

8 months ago | 4

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Answered
Eigenvectors are not orthogonal for some skew-symmetric matrices, why?
Your matrix A is _"defective"_ , meaning that its eigenvalues are not all distinct. In fact, it has only three distinct eigenva...

1 year ago | 1

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Answered
Sum of highest length of consecutive lowest values from a array.
L = min(A); f = find(diff([false,A==L,false])~=0); h = L*max(f(2:2:end)-f(1:2:end-1)); h is the highest sum of consec...

1 year ago | 0

Answered
What condition to use for checking whether at least a single negative element in a array?
Use the 'any' logical function. if any(A.*B<0) If you are dealing with an array, C, of more than one dimension, do this:...

1 year ago | 0

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Answered
How to Make a Matrix Diagonal with Matlab?
Call on Matlab's 'svd' function. Read about it at: https://www.mathworks.com/help/matlab/ref/svd.html or possible you n...

1 year ago | 0

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Finding if a vector is a subset
The following should be faster: m = size(a,2); n = size(b,2); for k = 1:n-m+1 s = all(a==b(k:k+m-1)); if s,...

1 year ago | 0

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Answered
How to plot level curves of f(x,y) = 2x^2 + 5y^2. f(x,y) = c for c = 1,2,3,4,5,6
Your "level" curves are all ellipses and can most easily be generated by: t = linspace(0,2*pi); x = sqrt(c/2)*cos(t); ...

1 year ago | 0

Answered
how to make a function (named pcc ) that solves the cartesian product of 2 strings A(with n elements) and B(with m elements)?
Assume A and B are row strings. C = [reshape(repmat(A,length(B),1),[],1),repmat(B(:),length(A),1)]; The two-element rows...

1 year ago | 0

Answered
how to create function half adder in matlab
If the input bits are numeric scalars or logical values, b1 and b2, then the sum bit, 's', would be: s = b1 xor b2; or e...

1 year ago | 0

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Answered
Using nested loops, write a Matlab program that goes through all elements of a matrix (2D array) and replaces every element that is either a multiple of 5 or 7 with -1.
Your test on a number x from your array can be: if round(x/5)==x/5 | round(x/7)==x/7 (Doing fprintf('-1') just prints ou...

1 year ago | 0

Answered
What is the output?
The vector x has only three elements, [0,.3,.6], so the 'for' instruction reads: for n = 4:2 Therefore the loop will not...

1 year ago | 0

Answered
Please help me convert equation to matlab code.
N = 100; % <-- Choose some large number s = x; for n = 2*N-1:-2:1 s = x - s*x^2/((n+2)*(n+1)); end (I t...

1 year ago | 0

Answered
Why am I getting Inf in my matrix
It is easily possible for two finite nonzero numbers to have a quotient so large that Matlab must give 'inf' as its value. For ...

1 year ago | 1

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Answered
Multiply a column by a number
Let Ar be the name of the array. Ar(:,6) = 4*Ar(:,6); What could be simpler? Since 4 is a scalar, it is automatically a...

1 year ago | 0

Answered
how to use nested for loop by grabbing one column and subtracting another column.
Your n value will be 1478, but in z(i,j+1) you have allowed the j+1 index to get as large as 1479 because you have "for j=1:1:n"...

1 year ago | 0

Answered
Why does y come out as one number?
The scalar result is caused by the use of matrix division rather than element-by-element division. Replace '/' by './'. Simila...

1 year ago | 0

Answered
Lagrange Interpolation code error
The message is caused by your not defining or properly entering the value of vector 'xi'.

1 year ago | 0

Answered
Trapezoidal rule to find total work?
I would think your code should be this: work = 0; for k = 2:length(t) work = work + (F(k)+F(k-1))/2*(v(k-1)+v(k))/2...

1 year ago | 0

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Answered
How to do polynomial differentiation
Let P be the usual Matlab row vector of coefficients of a polynomial. Then, (as we all learned in calculus,) the corresponding ...

1 year ago | 1

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Answered
convert two column matrices into one column matrix
In the example you gave do this: C = zeros(9,1); C(1:2:end) = A; C(2:2:end) = B; For a general answer you need to ...

1 year ago | 0

Answered
Does 'i' after value stand for 'index', and if so why does it appear as part of the answer?
The 'i' in your result indicates a complex answer. I assume you are familiar with complex numbers. The 'i' represents the squa...

1 year ago | 1

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Answered
Representing base 4 numbers as "random walks"
The Matlab function 'dec2base' can be used to covert integers to character strings involving the characters '0', '1', '2', and '...

1 year ago | 0

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How to generate a joint probability matrix from a data matrix
Call the data matrix D. Then the two columns of D(:,2:3) are X and Y. XY = sortrows(D(:,2:3)); F = find( [true,any(XY(1...

1 year ago | 0

Answered
How can I write a program that indicates a number if it is integer or not?
If n is your number, then round(n)==n is true if and only if n is an integer

1 year ago | 0

Answered
where can i use round function to make the function perfect
I would suggest initially multiplying both 'tendered' and 'price' by 100 and using 'round' on the result: tendered = round(...

1 year ago | 0

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Answered
if a & b
You can't use the "short circuit" forms of logical operations for operands other than scalars. The double symbol '&&' is the sh...

1 year ago | 1

Answered
How do I use an matrix of indices to reference values in another matrix without using a loop?
[a,b,c] = size(alltemps); % tempindex must be 1 x b x c savedtemp = reshape(alltemps(reshape(tempindex,1,[])+(0:a:a*(b*c-1...

1 year ago | 0

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Answered
Solving a system of integral equations numerically
@Lewis: I noticed that the integrands in both of your integrals become infinite at the upper limit of integration, and this can ...

1 year ago | 0

Answered
Solving a system of integral equations numerically
This is a problem you can solve using Matlab's 'fsolve' function. The fact that your objective function requires two numerical ...

1 year ago | 0

Answered
How to plot a circle centered on a line and passing through a point?
There are infinitely many ways a circle can be centered on a line and pass through a given point, except for the case when a lin...

1 year ago | 0

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