How to append float with 4 numbers after decimal?

Question

The printed numbers are very long as it can be seen when we run the code. The numbers appended are too long and displaying them in a table like format is not possible with the current result. How do we append float with only 4 numbers after decimal directly for pn, u, v and a ?

y = 1/2
b = 1/4

u = []
v = []

t = []
p = [0,25,43.3013,50,43.3013,25,0,0,0,0,0,0]

a = []

pn = []
pn.append(0)



x = 0.0
for i in range(11):
    z = 0.0 + x
    t.append(z)
    x = x + 0.1

m = 0.45594
k = 18
c = 0.2865

u.append(0)
v.append(0)


a.append((p[0]-c*v[0]-k*u[0])/m)

dt = 0.1

a1 =(m/(b*dt*dt)+y*c/(b*dt))
a2 = (m/(b*dt)+(y/b-1)*c)
a3 = (((1/(2*b))-1)*m + dt*((y/(2*b))-1)*c)
kn = k + a1


for i in range(len(t)-1):
    pn.append(p[i+1]+ a1*u[i] + a2*v[i] + a3*a[i])
    u.append(pn[i+1]/kn)
    v.append(y*(u[i+1]-u[i])/(b*dt) + (1-y/b)*v[i] + dt* (1-y/(2*b))*a[i])
    a.append((u[i+1]-u[i])/(b*dt*dt) - v[i]/(b*dt)-(1/(2*b)-1)*a[i])



print("ti\t\t"+"Pi\t\t"+"Pni\t\t"+"u''i\t\t"+"u'i\t\t"+"ui")
for i in range(len(t)):
    print(t[i],p[i],pn[i],a[i],v[i],u[i])

Maybe this will help - https://stackoverflow.com/questions/4518641/how-to-round-a-floating-point-number-up-to-a-certain-decimal-place#4519044 — Sid, Sep 21 '19 at 06:25
Possible duplicate of [How to round a floating point number up to a certain decimal place?](https://stackoverflow.com/questions/4518641/how-to-round-a-floating-point-number-up-to-a-certain-decimal-place) — Bogdan Doicin, Sep 21 '19 at 06:27

score 1 · Answer 1 · answered Sep 21 '19 at 06:38

1

Try this print

   `print("{0:.4f}".format(t[i]),"{0:.4f}".format(p[i]),"{0:.4f}".format(pn[i]),
    "{0:.4f}".format(a[i]),"{0:.4f}".format(v[i]),"{0:.4f}".format(u[i]))`

answered Sep 21 '19 at 06:38

Rahul Gupta

28
5

score 1 · Answer 2 · answered Sep 21 '19 at 06:59

Rounding numbers when you still need them for further calculations isn't a good idea since it can lead to numerical inaccuracies. Instead of rounding the numbers themselves you could consider formatting the numbers during printing. For example, to print the numbers in a nicely formatted table you could do something like

col_width = 10
ndecimals = 4
headers =  ["time", "p", "pn", "a", "v", "u"]
data = [t, p, pn, a, v, u]
# print header
for tt in headers:
    print(f'{tt:>{col_width}}', end='')
print()
print('-'*col_width*len(headers))
# print data
for fields in zip(*data):
    for field in fields:
        print(f'{field:{col_width}.{ndecimals}f}', end='')
    print()

Result

      time         p        pn         a         v         u
------------------------------------------------------------
    0.0000    0.0000    0.0000    0.0000    0.0000    0.0000
    0.1000   25.0000   25.0000   48.5187    2.4259    0.1213
    0.2000   43.3013  133.1779   64.3899    8.0714    0.6462
    0.3000   50.0000  350.4197   34.3673   13.0092    1.7002
    0.4000   43.3013  619.7712  -31.9927   13.1280    3.0071
    0.5000   25.0000  819.2410 -106.0045    6.2281    3.9749
    0.6000    0.0000  814.7317 -151.8705   -6.6657    3.9530
    0.7000    0.0000  550.8590  -93.6138  -18.9399    2.6727
    0.8000    0.0000  109.2240   -5.8938  -23.9153    0.5299
    0.9000    0.0000 -346.0107   79.0077  -20.2596   -1.6788
    1.0000    0.0000 -655.0597  131.5883   -9.7298   -3.1783

How to append float with 4 numbers after decimal?

2 Answers2