I am new in lisp programming and I am trying to compare a variable let's say op to the characters +,-,*,/. But in every way I write the correct result doesn't show up. How could I rewrite the following code:
(defun evaluate(op o1 o2)
(cond
( (string= op `+) (+ o1 o2))
( (string= op `-) (- o1 o2))
( (string= op `*) (* o1 o2))
( (string= op `/) (/ o1 o2))
)
)
the input is:
(print (calculate `(- * + 4 3 2 5)))
So I get in my function the operator characters. Don't mind the numbers.
To be sure here is the calculate function.
(defun calculate (l)
(if (and (numberp (car l)) (not (null l)) )
(car l)
( evaluate (car l) (calculate (cdr l) )
(calculate (cdr l) ) )
)
)
The way calculate is written, this evaluates (- (* (+ 4 4) (+ 4 4)) (* (+ 4 4) (+ 4 4))), which is 0. I don't know what you expect, but let's take a look at tracing (SO> is the repl prompt):
SO> (trace evaluate calculate)
(EVALUATE CALCULATE)
SO> (calculate '(- * + 4 3 2 5))
0: (SO::CALCULATE (- * + 4 3 2 5))
1: (SO::CALCULATE (* + 4 3 2 5))
2: (SO::CALCULATE (+ 4 3 2 5))
3: (SO::CALCULATE (4 3 2 5))
3: CALCULATE returned 4
3: (SO::CALCULATE (4 3 2 5))
3: CALCULATE returned 4
3: (SO::EVALUATE + 4 4)
3: EVALUATE returned 8
2: CALCULATE returned 8
2: (SO::CALCULATE (+ 4 3 2 5))
3: (SO::CALCULATE (4 3 2 5))
3: CALCULATE returned 4
3: (SO::CALCULATE (4 3 2 5))
3: CALCULATE returned 4
3: (SO::EVALUATE + 4 4)
3: EVALUATE returned 8
2: CALCULATE returned 8
2: (SO::EVALUATE * 8 8)
2: EVALUATE returned 64
1: CALCULATE returned 64
1: (SO::CALCULATE (* + 4 3 2 5))
2: (SO::CALCULATE (+ 4 3 2 5))
3: (SO::CALCULATE (4 3 2 5))
3: CALCULATE returned 4
3: (SO::CALCULATE (4 3 2 5))
3: CALCULATE returned 4
3: (SO::EVALUATE + 4 4)
3: EVALUATE returned 8
2: CALCULATE returned 8
2: (SO::CALCULATE (+ 4 3 2 5))
3: (SO::CALCULATE (4 3 2 5))
3: CALCULATE returned 4
3: (SO::CALCULATE (4 3 2 5))
3: CALCULATE returned 4
3: (SO::EVALUATE + 4 4)
3: EVALUATE returned 8
2: CALCULATE returned 8
2: (SO::EVALUATE * 8 8)
2: EVALUATE returned 64
1: CALCULATE returned 64
1: (SO::EVALUATE - 64 64)
1: EVALUATE returned 0
0: CALCULATE returned 0
0
That last 0 is the result. Of the numbers, only the first one is ever touched, and I guess you meant to use the others too.
It should be helpful to point out that the two calls to (calculate (cdr l)) inside of calculate will always produce the same result.
Side notes:
use standard formatting (see e. g. http://www.gigamonkeys.com/book/syntax-and-semantics.html#formatting-lisp-code)
use the apostrophe ', not the backtick. The latter has different uses.
understand the difference between symbols and strings
Related
In this table it's easy to find that column E is the first match for the value 3.
How do I find the column of the last match of 3 which will be column I
A B C D E F G H I J K L
6 6 9 9 3 3 2 2 3 1 1 1
Use this formula
=ArrayFormula(Substitute(Address(1,MAX(IF(REGEXMATCH(A1:L1,3&"")<>TRUE,,COLUMN(A1:L1))),4),"1",""))
try:
=SUBSTITUTE(ADDRESS(2, XMATCH(3, A2:P2,, -1), 4), 2, )
=ADDRESS(2, XMATCH(3, A2:P2,, -1), 4)
=XLOOKUP(3, A2:P2, A1:P1,,, -1)
XMATCH has a reverse search feature. Set search_mode top -1 to activate:
=INDEX(1:1,XMATCH(3,2:2,,-1))
(A1)A
B
C
D
E
F
G
H
I
J
K
L
6
6
9
9
3
3
2
2
3
1
1
1
Result:
I
I have a function in Maxima I am differentiating then attempting to find the value at which this is zero. When I use solve(), however, I am not given a solution. Why is this, and how can I work around it?
(%i1) f(x):=(-5*(x^4+5*x^3-3*x))/(x^2+1);
(%o1) f(x):=((-5)*(x^4+5*x^3+(-3)*x))/(x^2+1)
(%i2) df(x):=''(diff(f(x), x));
(%o2) df(x):=(10*x*(x^4+5*x^3-3*x))/(x^2+1)^2-(5*(4*x^3+15*x^2-3))/(x^2+1)
(%i3) solve(df(x), x);
(%o3) [0=2*x^5+5*x^4+4*x^3+18*x^2-3]
The function solve is not too strong; there are many problems it can't solve. A stronger version is under development. In the meantime, try the add-on package to_poly_solve. Here's what I get:
(%i1) df(x) := (10*x*(x^4+5*x^3-3*x))/(x^2+1)^2-(5*(4*x^3+15*x^2-3))/(x^2+1) $
(%i2) load (to_poly_solve) $
(%i3) to_poly_solve (df(x), x);
(%o3) %union([x = - 2.872468527640942], [x = - 0.4194144025323134],
[x = 0.3836388367122223], [x = 0.2041221431132173 - 1.789901606296292 %i],
[x = 1.789901606296292 %i + 0.2041221431132173])
Something which is maybe a little surprising is that to_poly_solve has returned a numerical solution instead of exact or symbolic. Tracing allroots shows that to_poly_solve has constructed a quintic equation and punted it to allroots. Since the general quintic doesn't have a solution in terms of radicals, and even in special cases it's probably very messy, maybe it's most useful to have a numerical solution anyway.
Try plot2d(df(x), [x, -3, 1]) to visualize the real roots returned above.
You can try to find a numerical solution. I don't know why solve does not try this. Either you take the ouput of aolveor you do hte folölowing:
(%i1) f(x):=(-5*(x^4+5*x^3-3*x))/(x^2+1);
4 3
(- 5) (x + 5 x + (- 3) x)
(%o1) f(x) := ---------------------------
2
x + 1
(%i2) df(x):=''(diff(f(x), x));
4 3 3 2
10 x (x + 5 x - 3 x) 5 (4 x + 15 x - 3)
(%o2) df(x) := ---------------------- - --------------------
2 2 2
(x + 1) x + 1
Bring it to a common denominator and extract the numerator:
(%i3) xthru(df(x));
4 3 2 3 2
10 x (x + 5 x - 3 x) - 5 (x + 1) (4 x + 15 x - 3)
(%o3) ------------------------------------------------------
2 2
(x + 1)
(%i4) num(%);
4 3 2 3 2
(%o4) 10 x (x + 5 x - 3 x) - 5 (x + 1) (4 x + 15 x - 3)
use allsrootsto find the roots of a polynomial numerically
(%i5) allroots(%);
(%o5) [x = 0.3836388391066617, x = - 0.4194143906217701,
x = 1.789901606296292 %i + 0.2041221431132174,
x = 0.2041221431132174 - 1.789901606296292 %i, x = - 2.872468734711326]
skip the complex solutions
(%i6) sublist(%,lambda([t],imagpart(rhs(t))=0))
;
(%o6) [x = 0.3836388391066617, x = - 0.4194143906217701,
x = - 2.872468734711326]
How to expand taylor series/polynomials about Q=0 , and then extract coefficients as a list
example :
taylor ( (sin(q)), q, 0, 9); //taylor expansion for first 9 terms gives the next line
(%o1)/T/ q\-q^3/6+q^5/120\-q^7/5040+q^9/362880+...
then using coeff ((%o1), q ^n); gives me the coefficient at n only, what i want is a list for all the coefficients of that expression
Try coeff plus makelist, e.g. something like: makelist(coeff(%o1, q, n), n, 0, 9);
Edit:
I see now that I misread your question and there is already an answer. Nevertheless I will keep it because it is related to your question.
Use powerseries instead of taylor:
(%i1) expr:powerseries(sin(x),x,0);
inf
==== i2 2 i2 + 1
\ (- 1) x
(%o1) > -----------------
/ (2 i2 + 1)!
====
i2 = 0
You can access the coefficient by the args or part function
(%i2) op(expr);
(%o2) sum
(%i3) args(expr);
i2 2 i2 + 1
(- 1) x
(%o3) [-----------------, i2, 0, inf]
(2 i2 + 1)!
(%i4) part(expr,1);
i2 2 i2 + 1
(- 1) x
(%o4) -----------------
(2 i2 + 1)!
(%i5) args(expr)[1];
i2 2 i2 + 1
(- 1) x
(%o5) -----------------
(2 i2 + 1)!
If you want to change the index variable:
(%i6) niceindices(expr),niceindicespref=[n];
inf
==== n 2 n + 1
\ (- 1) x
(%o6) > ---------------
/ (2 n + 1)!
====
n = 0
newbie Maxima question
I have a transfer function in Maxima
E1 : y = K_i*s/(s^2 + w^2);
I'd like to have the closed-form of the equation affter applying the bilinear transform
E2 : s = (2/Ts*(z-1)/(z+1));
I would like to get the transfer function for z, by substituing s by equation E2. How should I proceed?
Regards
Note that subst can apply one or more substitutions stated as equations. In this case, try subst(E2, E1).
That will probably create a messy result -- you can simplify it somewhat by applying ratsimp to the result.
Here's what I get from that.
(%i2) E1 : y = K_i*s/(s^2 + w^2);
K_i s
(%o2) y = -------
2 2
w + s
(%i3) E2 : s = (2/Ts*(z-1)/(z+1));
2 (z - 1)
(%o3) s = ----------
Ts (z + 1)
(%i4) subst (E2, E1);
2 K_i (z - 1)
(%o4) y = ------------------------------
2
4 (z - 1) 2
Ts (z + 1) (------------ + w )
2 2
Ts (z + 1)
(%i5) ratsimp (%);
2
2 K_i Ts z - 2 K_i Ts
(%o5) y = -----------------------------------------------
2 2 2 2 2 2 2
(Ts w + 4) z + (2 Ts w - 8) z + Ts w + 4
I am making a Common Lisp function to print the first N prime numbers. So far I've managed to write this code:
;globals
(setf isprime 1) ;if 1 then its a prime, 0 if not.
(setf from 1) ;start from 1
(setf count 0) ;should act as counter to check if we have already
; N primes printed
;function so far.
(defun prime-numbers (to)
(if (> count to) nil(progn
(is-prime from from)
(if (= isprime 1) (print from)(setf count (+ count 1)))
(setf isprime 1)
(setf from (+ from 1))
(prime-numbers to)))
(if (>= count to)(setf count 0) (setf from 1)))
;code to check if a number is prime
(defun is-prime(num val)
(if (< num 3) nil
(progn
(if (= (mod val (- num 1)) 0) (setf isprime 0))
(is-prime (- num 1) val))))
My problem is, it does not print N primes correctly.
If I call >(prime-numbers 10),
results are:
1
2
3
5
7
11
13
17
19
1,
i.e. it printed only 9 primes correctly.
but then if i call >(prime-numbers 2)
the results are: 1
2
3
5
7
1
what am I doing wrong here?? this is my first time to code in LISP.
UPDATE:
(defparameter from 1)
(defparameter count 0)
(defun prime-numbers (to)
(if (> count to)nil
(progn
(when (is-prime from)
(print from)
(setf count (+ count 1)))
(setf from (+ from 1))
(prime-numbers to)))
(when (>= count to)
(setf count 0)
(setf from 1)))
(defun is-prime (n)
(cond ((= 2 n) t)
((= 3 n) t)
((evenp n) nil)
(t
(loop for i from 3 to (isqrt n) by 2
never (zerop (mod n i))))))
works fine. but outputs a NIL at the end.
First, there's no need to use globals here, at all.
Use true/false return values. That would allow your is-prime function to be something like:
(defun is-prime (n)
(cond ((= 2 n) t) ;; Hard-code "2 is a prime"
((= 3 n) t) ;; Hard-code "3 is a prime"
((evenp n) nil) ;; If we're looking at an even now, it's not a prime
(t ;; If it is divisible by an odd number below its square root, it's not prime
(loop for i from 3 to (isqrt n) by 2
never (zerop (mod n i))))))
That way, the function is not relying on any external state and there's nothing that can confuse anything.
Second, the last 1 you see is (probably) the return value from the function.
To check that, try:
(progn (prime-numbers 10) nil)
Third, re-write your prime-numbers function to not use global variables.
Fourth, never create global variables with setf or setq, use either defvar or defparameter. It's also (mostly, but some disagree) good style to use *earmuffs* on your global (really, "special") variables.
To expand on Vatines answer:
A possible rewrite of the prime-numbers function, using the same algoritm but avoiding globals is
(defun prime-numbers (num &optional (from 2))
(cond ((<= num 0) nil)
((is-prime from) (cons from (prime-numbers (1- num) (1+ from))))
(t (prime-numbers num (1+ from)))))
This function also returns the primes instead of printing them.
The problem with this recursive solution is it consumes stack for each prime found/tested. Thus stack space may be exhausted for large values of num.
A non-recursive variant is
(defun prime-numbers (num &optional (start 2))
(loop for n upfrom start
when (is-prime n)
sum 1 into count
and collect n
until (>= count num)))