Is something like this what you are asking for?
%%
a = [100.001469926008 0.0140073495254864 0.00452326089811489 ...
, 0.00228582409151486 0.00157249586126199 0.00121055360392781 ...
, 0.000988328854777707 0.000836846113296335 0.000726496714817108 ];
%%
daff = diff(a);
ix = find( a<1, 1, 'first' ); % "worth below 1"
if all( daff(ix:end) < 0 ) % "keep decreasing"
a(ix:end)=0; % "changes to 0"
end
it returns
>> a
a =
Columns 1 through 5
100 0 0 0 0
Columns 6 through 9
0 0 0 0
Based on the comments below I think the best answer is:
%%
daff = diff(a);
if all( daff < 0 ) % "keep decreasing" monotonically decreasing
a(:) = 0; % "changes to 0" "(:)" is needed to replace ALL values by 0
end
