akellehe

Cryptographer

Part 1 - Decoding to binary format.

Write a script named char_to_bin.sh that takes a single commandline input argument and returns that argument encoded to binary. For example:

>> ./char_to_bin.sh "a"
1100001

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Matlab methods

• size(mat,dim) - Prints the size of a particular dimension of a matrix
• length(arr) - Output the scalar size of an array
• ones(x,y) - Create a vector/matrix of all ones
• zeros(x,y) - Create a vector/matrix of all zeros
• issparse(mat) - Returns 1 if the storage class is sparse
• diag(A), diag(v) - Returns a column vector of the diagonal elements of A or a square matrix with the elements of v as the diagonal elements (zeros elsewhere).
• sparse(A), sparse(m,n) - Creates a sparse matrix from the matrix A or an m by n sparse matrix of all zeros.
• [find(X>2), find(X>2)=0](http://www.

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import numpy
import math
import random

class Diffusion(object):
    def __init__(self, a_true, prob_model):
        N = numpy.size(a_true, 0)
        assert a_true.shape == (N,N), a_true.shape

        seed_node_index = math.floor(random.random() * N)

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Optimization

"Premature optimization is the root of all evil" 
                            -- DonaldKnuth

When we're coding we have to make tradeoffs between performance and readability. If you're making a decision where readability really suffers you should definitely consider whether or not your optimization is premature. Below we've attempted to identify a number of cases that are "readability-neutral" and improve performance.

Preamble

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def get_descendants(node, A, descendants=None):
    if not descendants:
        descendants = []

    descendants.append(node)

    children = A.getrow(node).indices
    for child in children:
        descendants += get_descendants(child, A)

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def get_descendants(node, A):
    unexplored = deque([node])
    descendants = set()
    while unexplored:
        node = unexplored.popleft()
        descendants.add(node)
        children = A.getrow(node).indices
        for child in children:
            unexplored.append(child)

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def get_descendants(node, A):
    unexplored = deque([node])
    while unexplored:
        node = unexplored.popleft()
        yield node
        children = A.getrow(node).indices
        for child in children:
            unexplored.append(child)

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class Node(object):
    def __init__(self, name):
        self.name = name
        self.children = []

    def add_child(self, child):
        self.children.append(child)

    def __repr__(self):
        return '<{0}>'.format(self.name)

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graph = []
for name in xrange(6):
    graph.append(Node(name))

graph[0].add_child(graph[1])
graph[0].add_child(graph[2])
graph[2].add_child(graph[3])
graph[2].add_child(graph[4])
graph[4].add_child(graph[5])

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def get_descendants(node):
    unexplored = deque([node])
    while unexplored:
        node = unexplored.popleft()
        yield node
        children = node.children
        for child in children:
            unexplored.append(child)