I want to define a function which returns a random number:
gnuplot> rnd() = int(rand(0)*2**24)
^
invalid command
I need add a parameter x to stop the error message:
gnuplot> rnd(x) = int(rand(0)*2**24)
Is it possible to define a function without parameters?
I don't think that is possible (look at the syntax for functions in help user-defined). As far as I can tell -- using rand is the only time when this is useful -- In all other cases your "function" would just evaluate to a constant. I'm guessing the gnuplot devs just haven't thought of this (interesting) corner case, or they didn't think it useful enough to implement.
I hope that I'm wrong about this and somebody else comes along and proves it, but I don't think I am. I think the easiest workaround it to just pass a parameter as you've already mentioned. If you really don't like that, you could use a macro:
set macro
rnd="(int(rand(0)*2**24))"
print 5+#rnd
Related
It probably has been asked before,
But I couldn't find something like that,
I'm trying to print a generator object:
n="12234451"
print(*[n[c]for c in range(len(n))if n[c]!=n[c-1]or c==0],sep="")
I usually use something like that, however, I'm wondering if it's the most efficient way to do it
(without changing the fact that the expression is in the print)
Thanks for your time
there is this method I used the other day and I have forgotten the details, which in we used a syntax like this:
f=//command//(x,'sin(x)');
something like this.
im not sure if the syntax is fully correct, or what the right command is. but after this we could simply ask for the f(x) value like this:
x= 0;
y= f(x);
and then the results were y=0;
What you are asking for is usually not recommendable. Please check if a simple anonymous function also fits your requirements:
f=#(x)(sin(x))
In case you really need to evaluate from a string:
f=str2func('#(x)sin(x)')
I would advice against the second option unless absolutely required, it can lead to hard to debug errors.
well I found the answer myself and it was "inline" command; :)
f=inline('sin(x+y+z)','x','y','z');
you can add as much variables as needed too.
I want to create a function that takes some chain of characters as an argument, and uses it as a str object.
def useless_function(argument) :
print(argument)
useless_function(banana)
--> NameError: name 'banana' is not defined
So this is what I did : I created a decorator that turns whatever I enter as argument into a str my function can print.
def decorator(f) :
def wrapper(arg_f) :
str_arg = str(arg)
f(str_arg)
return wrapper
So now I can decorate useless_function with my decorator, and useless_function(banana) will print 'banana'. And it will work with whatever it enter as an argument of useless_function.
My question is : is there a more elegant way or a simpler and faster way to do this automatic transformation into a string that can be used as an argument ?
Can you please elaborate because I don't understand what it is that you are looking for or saying.
If you mean: inside a function can you do input("variable")? Then the answer is yes. It is just essentially raw_input() from python2. The input from your keyboard will always be a str if I am not mistaken.
Update after edited post:
It is still not any more clear what you are trying to do.
At the end of the function, you do return * but I assume you know this.
I am really confused, but have you considered just doing str(argument)? As in takes_argument(str(argument))
2nd Update after 2nd edit:
I think I finally understand what you are trying to do, but I might be wrong.
Now, the problem is that def useless_function(argument) : will expect argument to be defined as a variable with some value(s). I am not aware of any other way than actually putting "argument" to tell python that what you are inserting is a string of characters rather than trying to reference some variable and its value. It is the same case as with print('something'), if I were to put print(something), python would try to look up the variable called something which you haven't defined.
Hope that makes sense.
I'm trying to do some simple fits using Gnuplot and encountering an error which somehow I'm not able to explain. Seems that I'm doing something terribly wrong with the definition of my function.
I first started with a fit of some functions. The functional form of these is not important as the fits work pretty well, but since they are involved later I'm reporting them as well.
evap(x)=(x>x_fc)?A*qnet(x)/wm2_to_mmh:(x<x_wp)?0:(A*qnet(x)/wm2_to_mmh)*(x-x_wp)/(x_fc-x_wp)
fit evap(x) './fluxes_da_1p0.txt' using 1:2 via A, x_fc, x_wp
sensible(x)=( (qnet(x)/wm2_to_mmh)-evap(x) ) / (1+B)+C
fit sensible(x) './fluxes_da_1p0.txt' using 1:3 via B,C
Then I defined
deltasensible(x)=abs(sensible(x)-sensible(0.454))
deltalatent(x)=abs(evap(x)-evap(0.454))
period_adv=18.0
g(x)=m*deltalatent(x)*period_adv*(deltasensible(x))**e
If I impose
m=3.8
e=0.5
and just plot the function g(x) superimposed on the data it seems to work pretty well.
However if I try to fit it using the parameters
fit g(x) './advection_da_1p0.txt' using 5:2 via m,e
I get the following error
iter chisq delta/lim lambda m e
0 4.2471983038e+00 0.00e+00 5.51e+00 3.800000e+00 5.000000e-01
1 3.7149813491e+00 -1.43e+04 5.51e-01 3.573384e+00 4.843345e-01
Current data point
=========================
# = 8 out of 8
x = 0.0178156
z = 0.0309726
Current set of parameters
=========================
m = 0.0178156
e = -0.0583802
"rain_estimate.gpl", line 52: Undefined value during function evaluation
For some reason Gnuplot is trying out really strange values for m,e, although I provided their initial values. If I remove the deltalatent(x) dependency everything is working fine. Am I missing something simple?
So I think I figured it out the problem by myself. Given my data a line was the best fit for Gnuplot so that it was trying to remove the exponential dependency on deltasensible by choosing a really small coefficient. Seems more an "error" with the data than with Gnuplot itself.
I want to represent a function like x->x^2 as a string - simply doing string(x->x^2) doesn't work, is there any way around this?
You could create a function from string using fun=eval(parse("x->x^2")) but as far as I know it's an irreversible process.
Just because something works, doesn't mean it is a solution... Suppose f is the anonymous function. With f = x->x^2. Then the following:
join(map(strip,match(r"line \d*:\n(.*)\n",string(f.code)).captures),"\n")
Gives:
return x ^ 2
More can be extracted using regular expressions from f.code. Also note this doesn't work for non-anonymous functions. And it isn't something one should rely on to work. Perhaps some other way to implement the functionality would be best.