This is the problem:
Write a function called top_right that takes two inputs: a matrix N and a scalar non-negative integer n, in that order, where each dimension of N is greater than or equal to n. The function returns the n-by-n square array at the top right corner of N.
My code:
function s=top_right(A,n)
s=A(1:n,end-n+1:end);
I dont know where I am wrong,
Thank you!
from your post and the corresponding commments its fair to assume you are new to MATLAB and stackoverflow. first to your question:
Your code works fine and does what it should, but i think it is somewhere it the script you work in. to use that as a function open a new script copy
function s=top_right(A,n)
s=A(1:n,end-n+1:end);
end
in there and save as 'top_right.m' (the name will be suggested when you save). while you work in that folder you can call your function with top_right(A,n)
Second on how to ask question here so you can get a correct answer quickly. Check https://stackoverflow.com/help/mcve and make your question look like it is described, like:
hey you beautiful people! i am trying to get the top_right function to work, which should return the top right part of a matrix. my code is:
A=[(1:10)'*(1:10)];
function s=top_right(A,n)
s=A(1:n,end-n+1:end);
end;
but leaves me with the error
Error: File: test.m Line: 1 Column: 1
Function definitions are not permitted in this context.
Welcome to stackoverflow!
Related
I have this script on 2 npcs but both choose the same random number (7) how do I make the Npcs choose their own number? I did try with self.math.random and it gave an error
so what would the solution be? will I have to create different variables for each npc related to the random function?
function Behavior:Awake()
math.randomseed (os.time())
self.destino = math.random( 1, 7 )
In the engine I work with it says to put self. for independence...
The fact that you call math.randomseed inside a function suggests to me that you're calling it every time you want a random number. The purpose of math.randomseed is to initialize the RNG, which means you're initializing the RNG multiple times, hence the repetition. Usually, you need to call math.randomseed exactly once in the entire program.
it says to put self. for independence...
That's not a great explanation of how self works. self is a function parameter that gets automatically declared when you declare a function with colon notation.
I'm trying to run a cobweb code in Mathematica and I need the following script:
ClearAll[CobwebPlot]
Options[CobwebPlot]=Join[{CobStyle->Automatic},Options[Graphics]];
CobwebPlot[f_,start_?NumericQ,n_,xrange:{xmin_,xmax_},opts:OptionsPattern[]]:=Module[{cob,x,g1,coor},
cob=NestList[f,N[start],n];
coor = Partition[Riffle[cob,cob],2,1];
coor[[1,2]]=0;
cobstyle=OptionValue[CobwebPlot,CobStyle];
cobstyle=If[cobstyle===Automatic,Red,cobstyle];
g1=Graphics[{cobstyle,Line[coor]}];
Show[{Plot[{x,f[x]},{x,xmin,xmax},PlotStyle->{{Thick,Black},Black}],g1},FilterRules[{opts},Options[Graphics]]]
]
Manipulate[CobwebPlot[Sqrt[3#-1]&,\[Alpha],40,{0,5},PlotRange->{{0,4.5},{0,3.65}},Frame->True,Axes->False,CobStyle->Directive[Dashed,Red],PlotRangePadding->None],{\[Alpha],0.5,4.375}]
I found the script online but I don't understand some features, such as what is the purpose of the following characters, # and &, in the Manipulate[] segment of the code:
Manipulate[CobwebPlot[Sqrt[3#-1]&,\[Alpha],40,{0,5},PlotRange->{{0,4.5},{0,3.65}},Frame->True,Axes->False,CobStyle->Directive[Dashed,Red],PlotRangePadding->None],{\[Alpha],0.5,4.375}]
Can you help me?
See this Mathematica documentation page on pure functions, or what other languages call anonymous functions, or lambda functions.
To give a cute example, suppose you have the function
doItTwice[x_,f_] := f[f[x]];
Now say you want to use this function to square the number seven twice. One way to do this would be to define a square function like this:
square[x_] := x^2;
doItTwice[7, square]
Well, there is a cleaner way to do this by simply writing the square function as a pure function, which would look like (#^2)&. The # is the parameter to the pure function, and the & is just there to indicate that it's a pure function. Really the parenthesis aren't even necessary, so you could write #^2&. Anyways, the following code is now a cleaner way to square seven twice:
doItTwice[7, (#^2)&]
I am trying to use the cg! function from IterativeSolvers.jl on for solving matrix-matrix linear systems, i.e. AX=B for A,X,B appropriately sized matrices. Given the way the indices work, X[:,i] is independent of all but B[:,i], and so this actually boils down to n different linear solves. Direct solving via \ works automatically in this case, but iterative solvers like CG don't. I can easily do this with a loop on the outside, but I haven't been able to get the in-place op working. For now, my code looks like this:
for j=1:size(u,2)
u[freenode,j],ch = cg!(u[freenode,j],lhs,Dinv.*rhs(u,i)[:,j]) # Requires Vector, need to change rhs
end
which gives solves CG with the appropriate lefthand side and righthand side. But the reason why it's not in-place boils down to this simple example throwing an error:
using IterativeSolvers
y = view(ones(4,2),:,2)
A=rand(4,4)
cg!(y,A,view(zeros(4,2),:,2))
which is:
ERROR: MethodError: no method matching init!
(::IterativeSolvers.KrylovSubspace{Float64,Array{Float64,2}}, ::SubArray{Float64,1,Array{Float64,2},Tuple{Colon,Int64},true})
Closest candidates are:
init!{T}(::IterativeSolvers.KrylovSubspace{T,OpT}, ::Array{T,1}) at C:\Users\Chris\.julia\v0.5\IterativeSolvers\src\krylov.jl:66
in #cg!#23 at C:\Users\Chris\.julia\v0.5\IterativeSolvers\src\cg.jl:7 [inlined]
in cg!(::SubArray{Float64,1,Array{Float64,2},Tuple{Colon,Int64},true}, ::Array{Float64,2}, ::SubArray{Float64,1,Array{Float64,2},Tuple{Colon,Int64},true}, ::Int64) at C:\Users\Chris\.julia\v0.5\IterativeSolvers\src\cg.jl:6 (repeats 2 times)
The problem seems to not be with the views, given the results of a previous SE question
I have doubts that you'll be able to avoid allocations, because the init! function is implemented as
function init!{T}(K::KrylovSubspace{T}, v::Vector{T})
# K.v = Vector{T}[all(v.==zero(T)) ? v : v/norm(v)]
K.v = Vector{T}[copy(v)]
end
and hence there's a copy anyway. Nevertheless, if you want this function to accept views, it should not be an issue to just modify the Vector to AbstractVector. (The function is simple enough that if you don't like to modify the package, you can just add a more general method yourself.)
You're right, it's not a "view" problem per se, the problem seems to be that the init! method seems to not have been defined in a way that can accept a 'view' (i.e. a SubArray type). The error suggests that "the closest candidate is"
init!{T}(::IterativeSolvers.KrylovSubspace{T,OpT}, ::Array{T,1})
(i.e. there's no method definition for a SubArray, only for a normal Array, and it appears there's no generic function / base case available to fall back on)
If you 'collect' the array first, then it works (presumably) as expected:
julia> cg!( collect(y), A, view(zeros(4,2),:,2))
([0.0752658,-0.693794,0.330172,0.437474],IterativeSolvers.ConvergenceHistory{Float64,Array{Float64,1}}(false,0.0,5,[0.249856,0.392572,0.401496,0.463142]))
except obviously that's of no use to you because you don't really get to change y as intended this way.
The only way I see around it if you're intent on keeping y as a view until that point, is to temporarily 'hack' it into a normal array inside cg! using a compound statement:
cg!((y = collect(y); y),A,view(zeros(4,2),:,2))
but, obviously, it's no longer a view at this point, so you'd have to update the original array it was a view into manually ...
I'm looking to integrate a function I am building, but the function would change each iteration based on a given input. For instance:
y=4e^(mx/4)
I would want to integrate with respect to x with a lower and upper bound, but the value of m would change. I know all my values of m.
Can I work with this? My initial assumption would be to use QROMB but that seems limited and unable to handle my issue.
QROMB (and other integrators) want a function of one variable, so you have to get the m in there through the back door. One way is with a common block:
function integrand,x
common int_common,int_m
return,4*exp(int_m*x/4)
end
function integrator,m,xlow,xhigh
common int_common,int_m
int_m=m
return,qromb('integrand',xlow,xhigh)
end
integrator(m,xlow,xhigh) will return the integral you want.
I am having a little problem here. In the code below is a function that has two arguments when I attempt to execute the functions i obtained this error
Undefined function or method for input
arguments of type 'double' (X,CX) as shown in (1).
the function is coded as below
[CX,sse]= (vgg_kmiter(X, CX)) ....(1)
can someone point me out where is the problem with this code?
note that the x is the input points in a columns which is integer and the CX is the center of clustering which is also integer.
Thank you
[CX,sse]= (vgg_kmiter(X, CX)) ....(1)
Is not a valid line of code.
[CX,sse]= (vgg_kmiter(X, CX));
is fine, though the outer parentheses aren't needed.
[CX,sse]= (vgg_kmiter(X, CX)) %....(1)
is fine as well - everything after the % sign is considered a comment