Matlab函数与Python函数对应关系

常用函数

imagesc函数

MATLAB中的imagesc函数相当于Python中的

1	plt.imshow(obs_im_global, extent=[0, 1, 0, 1])

imread函数

opencv的一个像素为：[B,G,R] ,matplotlib的一个像素为：[R,G,B]。MATLAB中的imread函数相当于opencv中的

1 2	obs_im = cv2.imread('../images/ian1.jpg') obs_im = obs_im[:, :, ::-1]

reshape函数

MATLAB中的reshape函数相当于numpy中的reshape时要加上参数order="F"

MATLAB：

>> mat = [1:12]

mat =

     1     2     3     4     5     6     7     8     9    10    11    12

>> reshape(mat,[3,4])

ans =

     1     4     7    10
     2     5     8    11
     3     6     9    12

numpy：

mat = np.arange(1,13)

mat

array([ 1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12])

r = np.reshape(mat,(3,4))

array([[ 1,  2,  3,  4],
       [ 5,  6,  7,  8],
       [ 9, 10, 11, 12]])

r.shape

(3, 4)

numpy加上修正参数

r = np.reshape(mat, (3,4), order="F")

r
array([[ 1,  4,  7, 10],
       [ 2,  5,  8, 11],
       [ 3,  6,  9, 12]])

cell

MATLAB中的cell在Python中存储的时候相当于List

NumPy for MATLAB users

该内容来自matlab-numpy

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
`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
`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
`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
`[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.*a`	`a*a`	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
`b = a`	`b = a.copy()`	Copy of a

Indexing and accessing elements (Python: slicing)

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
`a .* b`	`a * b` or `multiply(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)，a \ b先求的是inv(a)而不是pinv(a)
	`vdot(a,b)`	Vector dot product
	`cross(a,b)`	Cross product

Find; conditional indexing

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
`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
`diff(a)`	`diff(x, n=1, axis=0)`	Discrete difference function and approximate derivative
``		Solve differential equations

Fourier analysis

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
`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