I have the following problem - I need to minimize the sum in the maple. For example, suppose I have this:
EXPESSION:=A[0]+A[1]+A[2]+A[3]+A[4]+A[5];
And I want to use some function
someFunction(EXPRESSION);
which will return a symbol of the Sum (like sum(A[i], i = 0 .. 5));
Is some function like that exists?
Okay, I guess that you need something to compress an existing expession. If you're willing to specify the summand, index, and index range, then someFunction could subtract the terms and add the (unevaluated) Sum of those terms.
convert_to_Sum:= (ex, summand, index)->
simplify(ex - sum(summand, index) + Sum(summand, index))
;
Example:
ex:= A[0]+A[1]+A[2]+A[3]+A[4]+A[5];
convert_to_Sum(ex, A[i], i= 0..5);
Use Sum(A[i], i= 0..5)
Note that Sum is uppercase. I realize that this does not handle the case where the expression already exists, which may be what you are primarily interested in.
Related
I am trying to choose a random index for quicksort, but for some reason, the array is not sorting. In fact, the algorithm returns a different array (ex. input [2,1,4] and [1,1,4] is outputted) sometimes. Any help would be much appreciated. This algorithm works if, instead of choosing a random index, I always choose the first element of the array as the pivot.
def quicksort(array):
if len(array) < 2:
return array
else:
random_pivot_index = randint(0, len(array) - 1)
pivot = array[random_pivot_index]
less = [i for i in array[1:] if i =< pivot]
greater = [i for i in array[1:] if i > pivot]
return quicksort(less) + [pivot] + quicksort(greater)
less = [i for i in array[1:] if i =< pivot]
You're including elements equal to the pivot value in less here.
But here, you also include the pivot value explicitly in the result:
return quicksort(less) + [pivot] + quicksort(greater)
Instead try it with just:
return quicksort(less) + quicksort(greater)
Incidentally, though this does divide-and-conquer in the same way as QuickSort does, it's not really an implementation of that algorithm: Actual QuickSort sorts the elements in place - your version will suffer from the run-time overhead associated with allocating and concatenating the utility arrays.
I have the file "global power plants" with a column "capacity_in_mw" (with numbers 30, 100, 45, ...) and another column is "primary_fuel" (Coal, Hydro, Oil, Solar, Nuclear, Wind, Coal).
I can generate a map in function of "capacity_in_mw" by setting the condition
plotdata = data.query('capacity_in_mw > 50')
Now, I would like to generate a map in function of "primary_fuel". Because data is alphanumeric, how do I set up the condition?
Furthermore, when making the map, to assign color='black' for Coal, color='green' for Wind, color='yellow' for Solar, ... etc.
Python.
I am a novice, but I think I found the solution. It is more of an issue of syntax, to use the == in the query to identify the alphanumeric value.
plotdata = data.query('primary_fuel == "Hydro"')
Also, lesson learned in the future to dig more before posting a question.
As simple as in title. I have nx1 sized vector p. I'm interested in the maximum value of r = p/foo - floor(p/foo), with foo being a scalar, so I just call:
max_value = max(p/foo-floor(p/foo))
How can I get which value of p gave out max_value?
I thought about calling:
[max_value, max_index] = max(p/foo-floor(p/foo))
but soon I realised that max_index is pretty useless. I'm sorry asking this, real beginner here.
Having dropped the issue to pieces, I realized there's no unique corrispondence between values p and values in my related vector p/foo-floor(p/foo), so there's a logical issue rather than a language one.
However, given my input data, I know that the solution is unique. How can I fix this?
I ended up doing:
result = p(p/foo-floor(p/foo) == max(p/foo-floor(p/foo)))
Looks terrible, so if you know any other way...
Once you have the index, use it:
result = p(max_index)
You can create a new vector with your lets say "transformed" values:
p2 = (p/foo-floor(p/foo))
and then just use find to find the max values on p2:
max_index = find(p2 == max(p2))
that will return the index or indices of p2 with the max value of that operation, and finally just lookup the original value in p
p(max_index)
in 1 line, this is:
p(find((p/foo-floor(p/foo) == max((p/foo-floor(p/foo))))))
which is basically the same thing you did in the end :)
How do I sum different fields? I want to sum all of the information for material(1) ...so I want to add 5+4+6+300 but I am unsure how. Like is there another way besides just doing material(1).May + material(1).June etc....
material(1).May= 5;
material(1).June=4;
material(1).July=6;
material(1).price=300;
material(2).May=10;
material(2).price=550;
material(3).May=90;
You can use structfun for this:
result = sum( structfun(#(x)x, material(1)) );
The inner portion (structfun(#(x)x, material(1))) runs a function each individual field in the structure, and returns the results in an array. By using the identity function (#(x)x) we just get the values. sum of course does the obvious thing.
A slightly longer way to do this is to access each field in a loop. For example:
fNames = fieldnames(material(1));
accumulatedValue = 0;
for ix = 1:length(fNames)
accumulatedValue = accumulatedValue + material(1).(fNames{ix});
end
result = accumulatedValue
For some users this will be easier to read, although for expert users the first will be easier to read. The result and (approximate) performance are the same.
I think Pursuit's answer is very good, but here is an alternative off the top of my head:
sum( cell2mat( struct2cell( material(1) )));
We've got an array of values, and we would like to create another array whose values are not in the first one.
Example:
load('internet.mat')
The first column contains the values in MBs, we have thought in something like:
MB_no = setdiff(v, internet(:,1))
where v is a 0 vector whose length equals to the number of rows in internet.mat. But it just doesn't work.
So, how do we do this?
You need to specify the range of possible values to define what values are not in internet . Say the range is v = 1:10 then setdiff(v,internet(:,1)) will give you the values in 1:10 that are not in the first column of internet.
It seems as if you don't want the first column.
You can simply do:
MB_no=internet(:,2:end);
assuming internet(:,1) has only positive integers and you wish to find which are the integers in [1,...,max( internet(:,1) )] that do not appear in that range you can simply do
app = [];
app( internet(:,1) ) = 1;
MB_no = find( app == 0 );
This is somewhat like bucket sort.