Trying to use CoCalc (sage) to plot solutions to a function requiring a modulus

Question

I have the following code and error message. Something I am doing seems to be messing up the % function in the hb function. I'm not really sure what or how to fix it. Any ideas?

def h(n):
    if (n % 4 >= 0) and (n % 4 < 1):
            k = 1
    else:
        k = 0
    return k

def hb(n):
    if (((n/4) % 2) >= 0) and (((n/4) % 2) < 1):
        k = -1*h(n)
    else:
        k = h(n)
    return k

def dalembert(y,t):
    x = 0.5*hb(y-t)+0.5*hb(y+t) 
    return x 

import numpy as np

box1 = np.array([1,2,6,10,20])

for i in range(len(box1)):
    g=Graphics()
    g += plot(dalembert(x,box1[i]), (x, 0, 4), color='blue')
    g.show()

Error in lines 18-21 Traceback (most recent call last): File "/cocalc/lib/python2.7/site-packages/smc_sagews/sage_server.py", line 1188, in execute flags=compile_flags) in namespace, locals File "", line 3, in File "", line 2, in dalembert File "", line 2, in hb File "sage/structure/element.pyx", line 1925, in sage.structure.element.Element.mod (build/cythonized/sage/structure/element.c:13956) return coercion_model.bin_op(left, right, mod) File "sage/structure/coerce.pyx", line 1182, in sage.structure.coerce.CoercionModel_cache_maps.bin_op (build/cythonized/sage/structure/coerce.c:9827) return PyObject_CallObject(op, xy) File "sage/structure/element.pyx", line 1923, in sage.structure.element.Element.mod (build/cythonized/sage/structure/element.c:13921) return (left).mod(right) File "sage/structure/element.pyx", line 1958, in sage.structure.element.Element.mod (build/cythonized/sage/structure/element.c:14242) raise bin_op_exception('%', self, other) TypeError: unsupported operand parent(s) for %: 'Symbolic Ring' and 'Symbolic Ring'

William Stein William Stein · Accepted Answer · 2018-12-02T15:00:13

Try replacing g += plot(dalembert(x,box1[i]), (x, 0, 4), color='blue') with something like function d0(y): return dalembert(y,box1[i]); g += plot(d0, (x, 0, 4), color='blue')

The problem is that when you write dalembert(x,box1[i]) in your code, it is evaluated first before even getting to using that in a plot, and it's evaluated with x a symbolic, which breaks other things...

Trying to use CoCalc (sage) to plot solutions to a function requiring a modulus

1 Answers