Converting Python to Matlab

2017 10 24
3 个回答
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更新时间：2022 4 18
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0 个投票

Spent a few hours on trying to figure out why the outputs are different, no luck. Python and Matlab are in a txt file along with their outputs.
Suggestions on what I should be looking at to resolve the issue?

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Walter Roberson
Walter Roberson 2017-10-24
We do not have the data or NumPanels to test with.
Zach Dunagan
Zach Dunagan 2017-10-24
编辑：Zach Dunagan 2017-10-25
I figured it out.

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Andrei Bobrov
Andrei Bobrov 2017-10-24
编辑：Andrei Bobrov 2017-10-24

0 个投票

Small typo in MATLAB code in nu2
nu2 = atan2(-(xc(k)-xp(n))*sin(theta(k))+(yc(k)-yp(n))*cos(theta(n))+(xp(n+1)-xp(n))*sin(theta(n))-(yp(n+1)-yp(n))*cos(theta(n)),(xc(k)-xp(n))*cos(theta(n))+(yc(k)-yp(n))*sin(theta(n))-(xp(n+1)-xp(n))*...
cos(theta(n))-(yp(n+1)-yp(n))*sin(theta(n))); % fixed!

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Zach Dunagan
Zach Dunagan 2017-10-24
I figured it out. I don't need the multiplication, '\' in Python means '...' in Matlab. The nu2 = atan2(x1, x2) similar to this line of code in my script. atan2(yp(k+1)-yp(k), xp(k+1)-xp(k)).
Andrei Bobrov
Andrei Bobrov 2017-10-24
Stop Zach!
How?
cos(theta(n)-(yp(n+1)-yp(n))*sin(theta(n)))
or
cos(theta(n))-(yp(n+1)-yp(n))*sin(theta(n))

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Zach Dunagan
Zach Dunagan 2017-10-25
编辑：Walter Roberson 2017-10-25

0 个投票

How would I insert zeros in the diagonal line of these 128 x 128 matrices?
nSource = -(sin(theta-transpose(theta)))*ups + (cos(theta-transpose(theta)))*wps;
ftSource = cos(theta-transpose(theta))*ups + sin(theta-transpose(theta))*wps;
nVortex = sin(theta-transpose(theta))*upv + cos(theta-transpose(theta))*wpv;
tVortex = cos(theta-transpose(theta))*upv + sin(theta-transpose(theta))*wpv;

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Walter Roberson
Walter Roberson 2017-10-25
For the special case of square matrices, often the easiest way is
M - diag(diag(M))
For other matrices,
tril(M,1) + triu(M,1)
Zach Dunagan
Zach Dunagan 2017-10-26
What if I wanted to insert a number, other than zero?
Walter Roberson
Walter Roberson 2017-10-26
Just in case you have unsigned integers or the case where the existing value is so different from the new value that you have to worry about loss of precision:
Square matrix:
M(1:size(M,1)+1:end) = NewNumber;
Non-square matrix:
shorter = min(size(M,1),size(M,2));
lastidx = size(M,1)*(shorter-1)+shorter;
M(1:size(M,1)+1:lastidx) = NewNumber;
Zach Dunagan
Zach Dunagan 2017-10-26
M = M = nSource = 128 x 128 ?
Is the M inside of the size() the vector that lays in the diag of nSource?
Walter Roberson
Walter Roberson 2017-10-26
M is the array whose diagonal is to be set. For example,
nSource(1:size(nSource,1)+1:end) = NewNumber;
if nSource is square.
Zach Dunagan
Zach Dunagan 2017-10-26
编辑：Walter Roberson 2017-10-26
Actually this seem to have worked for my situation.
ups(logical(eye(size(ups)))) = 0;
wps(logical(eye(size(wps)))) = 0.5;
Zach Dunagan
Zach Dunagan 2017-10-26
编辑：Walter Roberson 2017-10-26
Can you please help me with the Matlab equivalent?
A=np.zeros((numPanels+1,numPanels+1))
A[:numPanels,:numPanels]=nSource
I just need the equivalent to this code.
A[:numPanels,-1]=np.sum(nVortex,axis=1)
Walter Roberson
Walter Roberson 2017-10-26
A[:numPanels,:numPanels]=nSource
would be
A(1:end-1, 1:end-1) = nSource;
I am not certain about
A[:numPanels,-1]=np.sum(nVortex,axis=1)
but I suspect
A(1:end-1, end) = sum(nVortex, 2);
Zach Dunagan
Zach Dunagan 2017-10-26
It worked! Thank you.
Zach Dunagan
Zach Dunagan 2017-10-26
A[-1,:numPanels]=tSource[0,:]+tSource[-1,:]
Here is what I have.
A(end, 1:end) = tSource(1, :) + tSource(end, :);
Error:
Subscripted assignment dimension mismatch.
Error in ssPanelMethod (line 112) A(end, 1:end) = tSource(1, :) + tSource(end, :);
Andrei Bobrov
Andrei Bobrov 2017-10-26
A(end, 1:end-1) = tSource(1, :) + tSource(end, :);
Zach Dunagan
Zach Dunagan 2017-10-28
编辑：Walter Roberson 2017-10-28
I really want to understand these little operations, rather than constantly asking for help here...
Python code
normVelFoil=np.dot(nSource,x[:-1])+np.dot(nVortex,x[-1]*np.ones((num
Panels,1)))+normU
tangVelFoil=np.dot(tSource,x[:-1])+np.dot(tVortex,x[-1]*np.ones((numPanels,1)))+tangU
Matlab code
normVelFoil = dot(nSource, x(1:end, 1:end-1)) + dot(nVortex, x(1:end, 1:end-1) * ones(numPanels, 1)) + normU;
tangVelFoil = dot(tSource, x(1:end, 1:end-1)) + dot(tVortex, x(1:emd, 1:end-1) * ones(numPanels, 1)) + tangU;
tSource, tVortex are 128 x 128, while x is a 129 x 1.
Zach Dunagan
Zach Dunagan 2017-10-28
编辑：Walter Roberson 2017-10-28
I changed dot to mtimes() or I could use .*
I compare the first dot to second dot of python and everything looks to be lining up. When I compare the normVelFoil outputs they don't line up.
Here is what I changed..
normVelFoil = mtimes(nSource, x(1:end-1, 1)) + mtimes(nVortex, x(end)*ones(numPanels, 1)) + normU;
Zach Dunagan
Zach Dunagan 2017-10-28
I have come to a conclusion the outputs are the same. They are both extremely small values, practically zero.

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ASHOK KUMAR MEENA
ASHOK KUMAR MEENA 2022-4-18

0 个投票

def Lagrange(x, y, n, xx):
sum = 0
for i in range(0, n + 1):
product = y[i]
for j in range(0, n + 1):
if (i != j):
product = product * (xx - x[j]) / (x[i] - x[j])
sum += product
return sum
def Trapezoidal(h, n, f):
sum = f[0]
for i in range (1, n):
sum = sum + 2 * f[i]
sum = sum + f[n]
ans = h * sum / 2
return ans

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