comp.soft-sys.math.mathematica Google Group

Re: Strange behavior when using pattern match and HoldAll

a...@gmx-topmail.de (Albert Retey) — Sun, 11 Nov 2009 12:27:20 UT

dnquark schrieb:
Because of the HoldAll attribute the argument is the symbol lst, not
it's value, the List {1,2,3}. This is why it doesn't match the pattern
_List but _Symbol and thus the function body is never executed. You can
check that this works:
Clear[test];
SetAttributes[test, HoldAll];
test[list_Symbol, val_] := list[[2]] = val;

Re: What is going on!?!

a...@gmx-topmail.de (Albert Retey) — Sun, 11 Nov 2009 12:27:04 UT

Joe Hays schrieb:
you are multiplying the result of the For loop with x, which happens to
be 10. And from the documentation:
"Unless an explicit Return is used, the value returned by For is Null."
which is why the result of the loop times 10 is 10*Null...
hth,
albert

Another Monitor problem

hanneskess...@hushmail.com (Hannes Kessler) — Sun, 11 Nov 2009 12:26:50 UT

Hello,
is it possible to monitor the intermediate state of a calculation with
Monitor inside the action argument of a Button? The following Monitor
example without a Button works:
Monitor[Do[i, {i, 10^7}], Refresh[Pause[0.03]; i, UpdateInterval ->
0.01]]
However, when the calculation is started by a Button only the final

Re: fitting

koop...@sfu.ca (Ray Koopman) — Sun, 11 Nov 2009 12:26:37 UT

You haven't said what your 'x' represents or how it is supposed to
relate to the Beta distribution. If we take the values as the counts
in equal-width bins that cover [0,1], then we can get the sample mean
and variance using the midpoints of the bins as the x-values, and use
the method of moments to estimate 'a' and 'b', the parameters of the

Re: What is going on!?!

d...@removedbailey.co.uk (David Bailey) — Sun, 11 Nov 2009 12:10:54 UT

Your For function returns Null, and this is getting multiplied by x
because you forgot the semicolon after the ] .
David Bailey
[link]

Re: Complex solutions to simple equations

d...@removedbailey.co.uk (David Bailey) — Sun, 11 Nov 2009 12:10:43 UT

Didn't your teacher tell you how to do this, or give you a reading list?
This board is not here to answer homework questions - what would be the
point?
David Bailey
[link]

Re: What is going on!?!

hanl...@cox.net (Bob Hanlon) — Sun, 11 Nov 2009 12:10:30 UT

The output of the For is Null (from documentation on For: "Unless an explicit Return is used, the value returned by For is Null."). When multiplied by x (i.e., 10) gives 10*Null. Put the semi-colon after the right bracket.
x = 0;
For[i = 1, i <= 10, i++, x = x + 1]; x
10
Bob Hanlon
=============
Can anyone tell me why the output is not a simple "10" instead of "10 Null"?

Re: What is going on!?!

readn...@sbcglobal.net (Bill Rowe) — Sun, 11 Nov 2009 12:08:45 UT

Per the documentation, For returns Null. So For[....] x
evaluates to x times Null which is what you got. If you want
simply the result then change the code to be:
=46or[i = 1, i <= 10, i++,
x = x + 1;
]; x
Or even better
Sum[n,,{n,10}]

Re: Can't figure out how to include syntax coloring in Printout

juneap...@gmail.com (Adam) — Sun, 11 Nov 2009 12:08:34 UT

Perfect - thanks, John.

Re: find subsets

readn...@sbcglobal.net (Bill Rowe) — Sun, 11 Nov 2009 12:08:23 UT

In[4]:= Cases[
Subsets[{a, b, c, d, e},
3], _?(Length[Intersection[#, {c, b}]] == 2 &)]
Out[4]= {{b,c},{a,b,c},{b,c,d},{b,c,e} }

Simplification problem

olfa.mra...@yahoo.fr (olfa) — Sun, 11 Nov 2009 12:08:11 UT

Hello mathematica community
Having this system of equations:
(z1==z2 && x*t==x1*t1)||(z1+x1*t1==z2+x2* t2)
why a function like fullsimplify or booleanminimize doesn't simplify
it into z1+x1*t1==z2+x2*t2?
same question for (y1==y2 && t1== t2)||(t1/2^y1==t2/2^y2) why it is
not simplified into t1/2^y1==t2/2^y2.

Re: find subsets

lsh...@gmail.com (Leonid Shifrin) — Sun, 11 Nov 2009 12:08:00 UT

Hi,
for initial set not too large, the following function should do:
Clear[getSubsets]
getSubsets[sets_List, all_List] :=
Select[sets, Complement[all, #] === {} &];
getSubsets[sets_List, all_List, {}] := getSubsets[sets, all];
getSubsets[sets_List, all_List, oneOf_List] :=
Select[getSubsets[sets, all], MemberQ[#, Alternatives @@ oneOf] &];

Re: find subsets

h...@together.net (Helen Read) — Sun, 11 Nov 2009 12:07:48 UT

It's a good practice to use names that begin with a lower case letter,
to avoid conflict with the names of built-in symbols and functions.
Select together with MemberQ will do the job. First, generate the subsets:
sets = Subsets[{a, b, c, d, e}, {3}]
This will select the ones that contain b:
Select[sets, MemberQ[#, b] &]

Re: What is going on!?!

djmp...@comcast.net (David Park) — Sun, 11 Nov 2009 12:07:36 UT

I think it is generally a good technique to put multiple statements in one
cell, but you need to insert a line return (Enter) before the last x. That
is, the last x should be on a separate line - but in the same cell.
Because of the last ";" the For statement returned a Null, which would
normally suppress output from a line, but you multiplied it by x and that's

Re: How can I reduce the frequency of a sine wave tia sal22

deg...@cwgsy.net (Chris Degnen) — Sun, 11 Nov 2009 12:06:39 UT

With a continuous, cyclic function it's a bit trivial:
a = Sin[10 x];
aim = Sin[5 x];
factor = (a + aim)/a - 1;
Plot[a*factor, {x, 0, 2 \[Pi]}]
For more complex cases you'd require deconvolution, e.g.
[link]
I'm looking forward to seeing any illustrative posts.