Shannon fano code error

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Maheen
Maheen 2015-10-15
编辑： Geoff Hayes 2015-10-20
function [sorted1 sorted2] = shannon_fano(keyword)
probabilities_calculation = zeros(size(keyword));
for i = 1:length(keyword) %find the probabilities of the symbols/occurence of each letter
probabilities_calculation(i) = (sum(keyword==keyword(i))/length(keyword));
end
[sorted1 sorted2] = shannon_split(probabilities_calculation);
function [first_half second_half] = shannon_split(input_symbols)
add_prob = 0;
for k = 1:length(input_symbols)
symbol1 = zeros(size(input_symbols));
if(input_symbols > 1)
add_prob = add_prob + input_symbols(k);
symbol1(k) = input_symbols(k);
if(sum(input_symbols)- add_prob <= 0.5)
first_half = zeros(size(symbol1(symbol1~=0)));
symbol2 = input_symbols(1:end) - symbol1; %now for the second half we consider the remaining elements
updated = symbol2(symbol2~=0);
second_half = ones(size(updated));
shannon_split(first_half);
shannon_split(second_half);
end
end
end
This is my code for shannon fano but i am receiving an error in it and is unable to solve it :(
This is the error:
Error in ==> shannon_fano>shannon_split at 15
add_prob = 0;
??? Output argument "first_half" (and maybe others) not assigned during call to
"D:\Matlab\shannon_fano.m (shannon_split)".
Error in ==> shannon_fano at 11
[sorted1 sorted2] = shannon_split(probabilities_calculation);
  1 个评论
Maheen
Maheen 2015-10-15
oh got it so if i use while instead of if then would it be fine? as i am getting error in that too

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回答（1 个）

Thorsten
Thorsten 2015-10-15
if(sum(input_symbols)- add_prob <= 0.5) if false, first_half and second_half are not computed in shannon_split, so the output arguments are not computed.
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显示 1更早的评论
Thorsten
Thorsten 2015-10-15
You have to ensure that for all input_symbols the values of both output parameters of your function are defined. So for this is only the case if at least once in your for loop the condition
(sum(input_symbols)- add_prob <= 0.5) i
becomes true.
Maheen
Maheen 2015-10-15
function mid = division(probabilities)
add_prob = 0;
for k = 1:length(probabilities) %go through the entire set
add_prob = add_prob + probabilities(k); %add single probability at a time
mid(k) = probabilities(k); %save the no of added probabilities
if(sum(probabilities)-add_prob <= 0.5)
break;
end
end
This is a code which i have improved for the division of probabilities so now where i can use the recursion technique so that i could repeat this task until we have only one element left

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