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NumPy for MATLAB users--matlab和python的不同

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NumPy for MATLAB users

Help

MATLAB/Octave	Python	Description
doc help -i % browse with Info	help()	Browse help interactively
help help or doc doc	help	Help on using help
help plot	help(plot) or ?plot	Help for a function
help splines or doc splines	help(pylab)	Help for a toolbox/library package
demo		Demonstration examples

Searching available documentation

MATLAB/Octave	Python	Description
lookfor plot		Search help files
help	help(); modules [Numeric]	List available packages
which plot	help(plot)	Locate functions

Using interactively

MATLAB/Octave	Python	Description
octave -q	ipython -pylab	Start session
TAB or M-?	TAB	Auto completion
foo(.m)	execfile('foo.py') or run foo.py	Run code from file
history	hist -n	Command history
diary on [..] diary off		Save command history
exit or quit	CTRL-D CTRL-Z # windows sys.exit()	End session

Operators

MATLAB/Octave	Python	Description
help -		Help on operator syntax

Arithmetic operators

MATLAB/Octave	Python	Description
a=1; b=2;	a=1; b=1	Assignment; defining a number
a + b	a + b or add(a,b)	Addition
a - b	a - b or subtract(a,b)	Subtraction
*a b**	*a b or multiply(a,b)**	Multiplication
a / b	a / b or divide(a,b)	Division
a .^ b	a ** b power(a,b) pow(a,b)	Power, $a^b$
rem(a,b)	a % b remainder(a,b) fmod(a,b)	Remainder
a+=1	a+=b or add(a,b,a)	In place operation to save array creation overhead
factorial(a)		Factorial, $n!$

Relational operators

MATLAB/Octave	Python	Description
a == b	a == b or equal(a,b)	Equal
a < b	a < b or less(a,b)	Less than
a > b	a > b or greater(a,b)	Greater than
a <= b	a <= b or less_equal(a,b)	Less than or equal
a >= b	a >= b or greater_equal(a,b)	Greater than or equal
a ~= b	a != b or not_equal(a,b)	Not Equal

Logical operators

MATLAB/Octave	Python	Description
a && b	a and b	Short-circuit logical AND
a \|\| b	a or b	Short-circuit logical OR
a & b or and(a,b)	logical_and(a,b) or a and b	Element-wise logical AND
a \| b or or(a,b)	logical_or(a,b) or a or b	Element-wise logical OR
xor(a, b)	logical_xor(a,b)	Logical EXCLUSIVE OR
~a or not(a) ~a or !a	logical_not(a) or not a	Logical NOT
any(a)		True if any element is nonzero
all(a)		True if all elements are nonzero

root and logarithm

MATLAB/Octave	Python	Description
sqrt(a)	math.sqrt(a)	Square root
log(a)	math.log(a)	Logarithm, base $e$ (natural)
log10(a)	math.log10(a)	Logarithm, base 10
log2(a)	math.log(a, 2)	Logarithm, base 2 (binary)
exp(a)	math.exp(a)	Exponential function

Round off

MATLAB/Octave	Python	Description
round(a)	around(a) or math.round(a)	Round
ceil(a)	ceil(a)	Round up
floor(a)	floor(a)	Round down
fix(a)	fix(a)	Round towards zero

Mathematical constants

MATLAB/Octave	Python	Description
pi	math.pi	$/pi=3.141592$
exp(1)	math.e or math.exp(1)	$e=2.718281$

Missing values; IEEE-754 floating point status flags

MATLAB/Octave	Python	Description
NaN	nan	Not a Number
Inf	inf	Infinity, $/infty$
	plus_inf	Infinity, $+/infty$
	minus_inf	Infinity, $-/infty$
	plus_zero	Plus zero, $+0$
	minus_zero	Minus zero, $-0$

Complex numbers

MATLAB/Octave	Python	Description
i	z = 1j	Imaginary unit
z = 3+4i	z = 3+4j or z = complex(3,4)	A complex number, $3+4i$
abs(z)	abs(3+4j)	Absolute value (modulus)
real(z)	z.real	Real part
imag(z)	z.imag	Imaginary part
arg(z)		Argument
conj(z)	z.conj(); z.conjugate()	Complex conjugate

Trigonometry

MATLAB/Octave	Python	Description
atan(a,b)	atan2(b,a)	Arctangent, $/arctan(b/a)$
	hypot(x,y)	Hypotenus; Euclidean distance

Generate random numbers

MATLAB/Octave	Python	Description
rand(1,10)	random.random((10,)) random.uniform((10,))	Uniform distribution
*2+5rand(1,10)**	random.uniform(2,7,(10,))	Uniform: Numbers between 2 and 7
rand(6)	random.uniform(0,1,(6,6))	Uniform: 6,6 array
randn(1,10)	random.standard_normal((10,))	Normal distribution

Vectors

MATLAB/Octave	Python	Description
a=[2 3 4 5];	a=array([2,3,4,5])	Row vector, $1 /times n$-matrix
adash=[2 3 4 5]';	array([2,3,4,5])[:,NewAxis] array([2,3,4,5]).reshape(-1,1) r_[1:10,'c']	Column vector, $m /times 1$-matrix

Sequences

MATLAB/Octave	Python	Description
1:10	arange(1,11, dtype=Float) range(1,11)	1,2,3, ... ,10
0:9	arange(10.)	0.0,1.0,2.0, ... ,9.0
1:3:10	arange(1,11,3)	1,4,7,10
10:-1:1	arange(10,0,-1)	10,9,8, ... ,1
10:-3:1	arange(10,0,-3)	10,7,4,1
linspace(1,10,7)	linspace(1,10,7)	Linearly spaced vector of n=7 points
reverse(a)	a[::-1] or	Reverse
a(:) = 3	a.fill(3), a[:] = 3	Set all values to same scalar value

Concatenation (vectors)

MATLAB/Octave	Python	Description
[a a]	concatenate((a,a))	Concatenate two vectors
[1:4 a]	concatenate((range(1,5),a), axis=1)

Repeating

MATLAB/Octave	Python	Description
[a a]	concatenate((a,a))	1 2 3, 1 2 3
	a.repeat(3) or	1 1 1, 2 2 2, 3 3 3
	a.repeat(a) or	1, 2 2, 3 3 3

Miss those elements out

MATLAB/Octave	Python	Description
a(2:end)	a[1:]	miss the first element
a([1:9])		miss the tenth element
a(end)	a[-1]	last element
a(end-1:end)	a[-2:]	last two elements

Maximum and minimum

MATLAB/Octave	Python	Description
max(a,b)	maximum(a,b)	pairwise max
max([a b])	concatenate((a,b)).max()	max of all values in two vectors
[v,i] = max(a)	v,i = a.max(0),a.argmax(0)

Vector multiplication

MATLAB/Octave	Python	Description
*a.a**	*aa**	Multiply two vectors
dot(u,v)	dot(u,v)	Vector dot product, $u /cdot v$

Matrices

MATLAB/Octave	Python	Description
a = [2 3;4 5]	a = array([[2,3],[4,5]])	Define a matrix

Concatenation (matrices); rbind and cbind

MATLAB/Octave	Python	Description
[a ; b]	concatenate((a,b), axis=0) vstack((a,b))	Bind rows
[a , b]	concatenate((a,b), axis=1) hstack((a,b))	Bind columns
	concatenate((a,b), axis=2) dstack((a,b))	Bind slices (three-way arrays)
[a(:), b(:)]	concatenate((a,b), axis=None)	Concatenate matrices into one vector
[1:4 ; 1:4]	concatenate((r_[1:5],r_[1:5])).reshape(2,-1) vstack((r_[1:5],r_[1:5]))	Bind rows (from vectors)
[1:4 ; 1:4]'		Bind columns (from vectors)

Array creation

MATLAB/Octave	Python	Description
zeros(3,5)	zeros((3,5),Float)	0 filled array
	zeros((3,5))	0 filled array of integers
ones(3,5)	ones((3,5),Float)	1 filled array
*ones(3,5)9**		Any number filled array
eye(3)	identity(3)	Identity matrix
diag([4 5 6])	diag((4,5,6))	Diagonal
magic(3)		Magic squares; Lo Shu
	a = empty((3,3))	Empty array

Reshape and flatten matrices

MATLAB/Octave	Python	Description
reshape(1:6,3,2)';	arange(1,7).reshape(2,-1) a.setshape(2,3)	Reshaping (rows first)
reshape(1:6,2,3);	arange(1,7).reshape(-1,2).transpose()	Reshaping (columns first)
a'(:)	a.flatten() or	Flatten to vector (by rows, like comics)
a(:)	a.flatten(1)	Flatten to vector (by columns)
vech(a)		Flatten upper triangle (by columns)

Shared data (slicing)

MATLAB/Octave	Python	Description
b = a	b = a.copy()	Copy of a

Indexing and accessing elements (Python: slicing)

MATLAB/Octave	Python	Description
a = [ 11 12 13 14 ... 21 22 23 24 ... 31 32 33 34 ]	a = array([[ 11, 12, 13, 14 ], [ 21, 22, 23, 24 ], [ 31, 32, 33, 34 ]])	Input is a 3,4 array
a(2,3)	a[1,2]	Element 2,3 (row,col)
a(1,:)	a[0,]	First row
a(:,1)	a[:,0]	First column
a([1 3],[1 4]);	a.take([0,2]).take([0,3], axis=1)	Array as indices
a(2:end,:)	a[1:,]	All, except first row
a(end-1:end,:)	a[-2:,]	Last two rows
a(1:2:end,:)	a[::2,:]	Strides: Every other row
	a[...,2]	Third in last dimension (axis)
a(:,[1 3 4])	a.take([0,2,3],axis=1)	Remove one column
	a.diagonal(offset=0)	Diagonal

Assignment

MATLAB/Octave	Python	Description
a(:,1) = 99	a[:,0] = 99
a(:,1) = [99 98 97]'	a[:,0] = array([99,98,97])
a(a>90) = 90;	(a>90).choose(a,90) a.clip(min=None, max=90)	Clipping: Replace all elements over 90
	a.clip(min=2, max=5)	Clip upper and lower values

Transpose and inverse

MATLAB/Octave	Python	Description
a'	a.conj().transpose()	Transpose
a.' or transpose(a)	a.transpose()	Non-conjugate transpose
det(a)	linalg.det(a) or	Determinant
inv(a)	linalg.inv(a) or	Inverse
pinv(a)	linalg.pinv(a)	Pseudo-inverse
norm(a)	norm(a)	Norms
eig(a)	linalg.eig(a)[0]	Eigenvalues
svd(a)	linalg.svd(a)	Singular values
chol(a)	linalg.cholesky(a)	Cholesky factorization
[v,l] = eig(a)	linalg.eig(a)[1]	Eigenvectors
rank(a)	rank(a)	Rank

Sum

MATLAB/Octave	Python	Description
sum(a)	a.sum(axis=0)	Sum of each column
sum(a')	a.sum(axis=1)	Sum of each row
sum(sum(a))	a.sum()	Sum of all elements
	a.trace(offset=0)	Sum along diagonal
cumsum(a)	a.cumsum(axis=0)	Cumulative sum (columns)

Sorting

MATLAB/Octave	Python	Description
a = [ 4 3 2 ; 2 8 6 ; 1 4 7 ]	a = array([[4,3,2],[2,8,6],[1,4,7]])	Example data
sort(a(:))	a.ravel().sort() or	Flat and sorted
sort(a)	a.sort(axis=0) or msort(a)	Sort each column
sort(a')'	a.sort(axis=1)	Sort each row
sortrows(a,1)	a[a[:,0].argsort(),]	Sort rows (by first row)
	a.ravel().argsort()	Sort, return indices
	a.argsort(axis=0)	Sort each column, return indices
	a.argsort(axis=1)	Sort each row, return indices

Maximum and minimum

MATLAB/Octave	Python	Description
max(a)	a.max(0) or amax(a [,axis=0])	max in each column
max(a')	a.max(1) or amax(a, axis=1)	max in each row
max(max(a))	a.max() or	max in array
[v i] = max(a)		return indices, i
max(b,c)	maximum(b,c)	pairwise max
cummax(a)
	a.ptp(); a.ptp(0)	max-to-min range

Matrix manipulation

MATLAB/Octave	Python	Description
fliplr(a)	fliplr(a) or a[:,::-1]	Flip left-right
flipud(a)	flipud(a) or a[::-1,]	Flip up-down
rot90(a)	rot90(a)	Rotate 90 degrees
repmat(a,2,3) kron(ones(2,3),a)	kron(ones((2,3)),a)	Repeat matrix: [ a a a ; a a a ]
triu(a)	triu(a)	Triangular, upper
tril(a)	tril(a)	Triangular, lower

Equivalents to "size"

MATLAB/Octave	Python	Description
size(a)	a.shape or a.getshape()	Matrix dimensions
size(a,2) or length(a)	a.shape[1] or size(a, axis=1)	Number of columns
length(a(:))	a.size or size(a[, axis=None])	Number of elements
ndims(a)	a.ndim	Number of dimensions
	a.nbytes	Number of bytes used in memory

Matrix- and elementwise- multiplication

MATLAB/Octave	Python	Description
*a . b**	*a b ormultiply(a,b)**	Elementwise operations
*a b**	matrixmultiply(a,b)	Matrix product (dot product)
	inner(a,b) or	Inner matrix vector multiplication $a/cdot b'$
	outer(a,b) or	Outer product
kron(a,b)	kron(a,b)	Kronecker product
a / b		Matrix division, $b{/cdot}a^{-1}$
a / b	linalg.solve(a,b)	Left matrix division, $b^{-1}{/cdot}a$ /newline (solve linear equations)
	vdot(a,b)	Vector dot product
	cross(a,b)	Cross product

Find; conditional indexing

MATLAB/Octave	Python	Description
find(a)	a.ravel().nonzero()	Non-zero elements, indices
[i j] = find(a)	(i,j) = a.nonzero() (i,j) = where(a!=0)	Non-zero elements, array indices
[i j v] = find(a)	v = a.compress((a!=0).flat) v = extract(a!=0,a)	Vector of non-zero values
find(a>5.5)	(a>5.5).nonzero()	Condition, indices
	a.compress((a>5.5).flat)	Return values
*a . (a>5.5)**	*where(a>5.5,0,a) or a (a>5.5)**	Zero out elements above 5.5
	a.put(2,indices)	Replace values

Multi-way arrays

MATLAB/Octave	Python	Description
a = cat(3, [1 2; 1 2],[3 4; 3 4]);	a = array([[[1,2],[1,2]], [[3,4],[3,4]]])	Define a 3-way array
a(1,:,:)	a[0,...]

File input and output

MATLAB/Octave	Python	Description
f = load('data.txt')	f = fromfile("data.txt") f = load("data.txt")	Reading from a file (2d)
f = load('data.txt')	f = load("data.txt")	Reading from a file (2d)
x = dlmread('data.csv', ';')	f = load('data.csv', delimiter=';')	Reading fram a CSV file (2d)
save -ascii data.txt f	save('data.csv', f, fmt='%.6f', delimiter=';')	Writing to a file (2d)
	f.tofile(file='data.csv', format='%.6f', sep=';')	Writing to a file (1d)
	f = fromfile(file='data.csv', sep=';')	Reading from a file (1d)

Plotting

Basic x-y plots

MATLAB/Octave	Python	Description
plot(a)	plot(a)	1d line plot
plot(x(:,1),x(:,2),'o')	plot(x[:,0],x[:,1],'o')	2d scatter plot
plot(x1,y1, x2,y2)	plot(x1,y1,'bo', x2,y2,'go')	Two graphs in one plot
plot(x1,y1) hold on plot(x2,y2)	plot(x1,y1,'o') plot(x2,y2,'o') show() # as normal	Overplotting: Add new plots to current
subplot(211)	subplot(211)	subplots
plot(x,y,'ro-')	plot(x,y,'ro-')	Plotting symbols and color

Axes and titles

MATLAB/Octave	Python	Description
grid on	grid()	Turn on grid lines
axis equal axis('equal') replot	figure(figsize=(6,6))	1:1 aspect ratio
axis([ 0 10 0 5 ])	axis([ 0, 10, 0, 5 ])	Set axes manually
title('title') xlabel('x-axis') ylabel('y-axis')		Axis labels and titles
	text(2,25,'hello')	Insert text

Log plots

MATLAB/Octave	Python	Description
semilogy(a)	semilogy(a)	logarithmic y-axis
semilogx(a)	semilogx(a)	logarithmic x-axis
loglog(a)	loglog(a)	logarithmic x and y axes

Filled plots and bar plots

MATLAB/Octave	Python	Description
fill(t,s,'b', t,c,'g') % fill has a bug?	fill(t,s,'b', t,c,'g', alpha=0.2)	Filled plot

Functions

MATLAB/Octave	Python	Description
f = inline('sin(x/3) - cos(x/5)')		Defining functions
ezplot(f,[0,40]) fplot('sin(x/3) - cos(x/5)',[0,40]) % no ezplot	x = arrayrange(0,40,.5) y = sin(x/3) - cos(x/5) plot(x,y, 'o')	Plot a function for given range

Polar plots

MATLAB/Octave	Python	Description
theta = 0:.001:2pi; r = sin(2theta);	theta = arange(0,2pi,0.001) r = sin(2theta)
polar(theta, rho)	polar(theta, rho)

Histogram plots

MATLAB/Octave	Python	Description
hist(randn(1000,1))
hist(randn(1000,1), -4:4)
plot(sort(a))

3d data

Contour and image plots

MATLAB/Octave	Python	Description
contour(z)	levels, colls = contour(Z, V, origin='lower', extent=(-3,3,-3,3)) clabel(colls, levels, inline=1, fmt='%1.1f', fontsize=10)	Contour plot
contourf(z); colormap(gray)	contourf(Z, V, cmap=cm.gray, origin='lower', extent=(-3,3,-3,3))	Filled contour plot
image(z) colormap(gray)	im = imshow(Z, interpolation='bilinear', origin='lower', extent=(-3,3,-3,3))	Plot image data
	# imshow() and contour() as above	Image with contours
quiver()	quiver()	Direction field vectors

Perspective plots of surfaces over the x-y plane

MATLAB/Octave	Python	Description
n=-2:.1:2; [x,y] = meshgrid(n,n); z=x.*exp(-x.^2-y.^2);	n=arrayrange(-2,2,.1) [x,y] = meshgrid(n,n) z = xpower(math.e,-x2-y*2)
mesh(z)		Mesh plot
surf(x,y,z) or surfl(x,y,z) % no surfl()		Surface plot

Scatter (cloud) plots

MATLAB/Octave	Python	Description
plot3(x,y,z,'k+')		3d scatter plot

Save plot to a graphics file

MATLAB/Octave	Python	Description
plot(1:10) print -depsc2 foo.eps gset output "foo.eps" gset terminal postscript eps plot(1:10)	savefig('foo.eps')	PostScript
	savefig('foo.pdf')	PDF
	savefig('foo.svg')	SVG (vector graphics for www)
print -dpng foo.png	savefig('foo.png')	PNG (raster graphics)

Data analysis

Set membership operators

MATLAB/Octave	Python	Description
a = [ 1 2 2 5 2 ]; b = [ 2 3 4 ];	a = array([1,2,2,5,2]) b = array([2,3,4]) a = set([1,2,2,5,2]) b = set([2,3,4])	Create sets
unique(a)	unique1d(a) unique(a) set(a)	Set unique
union(a,b)	union1d(a,b) a.union(b)	Set union
intersect(a,b)	intersect1d(a) a.intersection(b)	Set intersection
setdiff(a,b)	setdiff1d(a,b) a.difference(b)	Set difference
setxor(a,b)	setxor1d(a,b) a.symmetric_difference(b)	Set exclusion
ismember(2,a)	2 in a setmember1d(2,a) contains(a,2)	True for set member

Statistics

MATLAB/Octave	Python	Description
mean(a)	a.mean(axis=0) mean(a [,axis=0])	Average
median(a)	median(a) or median(a [,axis=0])	Median
std(a)	a.std(axis=0) or std(a [,axis=0])	Standard deviation
var(a)	a.var(axis=0) or var(a)	Variance
corr(x,y)	correlate(x,y) or corrcoef(x,y)	Correlation coefficient
cov(x,y)	cov(x,y)	Covariance

Interpolation and regression

MATLAB/Octave	Python	Description
z = polyval(polyfit(x,y,1),x) plot(x,y,'o', x,z ,'-')	(a,b) = polyfit(x,y,1) plot(x,y,'o', x,a*x+b,'-')	Straight line fit
a = x/y	linalg.lstsq(x,y)	Linear least squares $y = ax + b$
polyfit(x,y,3)	polyfit(x,y,3)	Polynomial fit

Non-linear methods

Polynomials, root finding

MATLAB/Octave	Python	Description
	poly()	Polynomial
roots([1 -1 -1])	roots()	Find zeros of polynomial
f = inline('1/x - (x-1)') fzero(f,1)		Find a zero near $x = 1$
solve('1/x = x-1')		Solve symbolic equations
polyval([1 2 1 2],1:10)	polyval(array([1,2,1,2]),arange(1,11))	Evaluate polynomial

Differential equations

MATLAB/Octave	Python	Description
diff(a)	diff(x, n=1, axis=0)	Discrete difference function and approximate derivative
		Solve differential equations

Fourier analysis

MATLAB/Octave	Python	Description
fft(a)	fft(a) or	Fast fourier transform
ifft(a)	ifft(a) or	Inverse fourier transform
	convolve(x,y)	Linear convolution

Symbolic algebra; calculus

MATLAB/Octave	Python	Description
factor()		Factorization

Programming

MATLAB/Octave	Python	Description
.m	.py	Script file extension
% % or #	#	Comment symbol (rest of line)
% must be in MATLABPATH % must be in LOADPATH	from pylab import *	Import library functions
string='a=234'; eval(string)	string="a=234" eval(string)	Eval

Loops

MATLAB/Octave	Python	Description
for i=1:5; disp(i); end	for i in range(1,6): print(i)	for-statement
for i=1:5 disp(i) disp(i*2) end	for i in range(1,6): print(i) print(i*2)	Multiline for statements

Conditionals

MATLAB/Octave	Python	Description
if 1>0 a=100; end	if 1>0: a=100	if-statement
if 1>0 a=100; else a=0; end		if-else-statement

Debugging

MATLAB/Octave	Python	Description
ans		Most recent evaluated expression
whos or who		List variables loaded into memory
clear x or clear [all]		Clear variable $x$ from memory
disp(a)	print a	Print

Working directory and OS

MATLAB/Octave	Python	Description
dir or ls	os.listdir(".")	List files in directory
what	*grep.grep(".py")**	List script files in directory
pwd	os.getcwd()	Displays the current working directory
cd foo	os.chdir('foo')	Change working directory
!notepad system("notepad")	os.system('notepad') os.popen('notepad')	Invoke a System Command

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