# Subscripted assignment dimension mismatch

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DAVIES on 8 Aug 2023
Edited: Walter Roberson on 8 Aug 2023
function [power_alloc, sum_rate] = power_allocation_noma(channel_gains, target_rates, total_power)
% channel_gains: Matrix of channel gains for each user and subchannel
% target_rates: Target rates for each user
% total_power: Total available power
[num_users, num_subchannels] = size(channel_gains);
% Initialize power allocation matrix
power_alloc = zeros(num_users, num_subchannels);
for u = 1:num_users
% Calculate interference from other users on each subchannel
interference = sum(power_alloc(:, setdiff(1:num_subchannels, u)) .* channel_gains(:, setdiff(1:num_subchannels, u)), 2);
% Calculate power allocation using water-filling algorithm
lagrange_multiplier = (target_rates(u) - interference) / channel_gains(u, u);
allocated_power = max(lagrange_multiplier, 0);
% Allocate the calculated power to all subchannels for the user
power_alloc(u, :) = allocated_power * ones(1, num_subchannels);
end
% Calculate sum rate
sum_rate = sum(log2(1 + power_alloc .* channel_gains), 'all');
I get this error:
subscripted assignment dimension mismatch.
Error in power_allocation_noma (line 20)
power_alloc(u, :) = allocated_power * ones(1, num_subchannels);
Error in main2 (line 13)
[power_alloc, sum_rate] = power_allocation_noma(channel_gains, target_rates, total_power);

Florian Bidaud on 8 Aug 2023
Edited: Florian Bidaud on 8 Aug 2023
This is because your interference variable is a 1*num_users vector, leading to lagrange_multiplier also being a 1*num_users vector. Thus allocated_power * ones(1, num_subchannels) is a num_subchannels*num_users matrix.
In the end you try to affect a num_subchannels*num_users matrix to a 1*num_subchannels vector.
The dimensions of the left and right side of the "=" are different
I think you can have what you seek with changing allocated power definiton to :
allocated_power = max(max(lagrange_multiplier, 0));

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