TypeError:'numpy.float64'对象不支持项目分配-类似的代码，错误引发 [英] TypeError: 'numpy.float64' object does not support item assignment - Similar code, error raises

问题描述

我正在编写分子动力学代码，为此，我有一个函数可以计算粒子之间的力:保守力，随机力和耗散力.保守力是成对的力，这意味着我有一个双循环来计算它们.我想节省一些时间，并在双循环的其中一个循环中包括随机力和耗散力的计算，如下所示:

I am writing a Molecular Dynamics code and for that I have a function that computes forces between particles: conservative, random and dissipative forces. The conservative forces are pairwise forces, which means I have a double loop for to compute them. I wanted to save some time and include the calculation of the random and dissipative forces in one of the loops of the double loop as follows:

fr = np.zeros((npart, dim))
fd = np.zeros((npart, dim))
fc = np.zeros((npart, dim))

for i in range(npart-1):

    for d in range(dim):
        # dissipative and random forces
        fd[i, d] = -gamma * v[i, d]
        fr[i, d] = noise/np.sqrt(dt) * np.random.normal()

    for j in range(i+1, npart):

        # conservative force for particle i
        fc[i, 0] = fc[i, 0] + (dX/r2) * fr
        fc[i, 1] = fc[i, 1] + (dY/r2) * fr
        fc[i, 2] = fc[i, 2] + (dZ/r2) * fr

        # conservative force for particle j (action-reaction)
        fc[j, 0] = fc[j, 0] - (dX/r2) * fr
        fc[j, 1] = fc[j, 1] - (dY/r2) * fr
        fc[j, 2] = fc[j, 2] - (dZ/r2) * fr

此处，伽马，噪声和dt是常数.我收到以下错误:

Here gamma, noise and dt are constants. I get the following error:

    fr[i, d] = noise/np.sqrt(dt)*np.random.normal()
TypeError: 'numpy.float64' object does not support item assignment

尽管如此，如果我在一个外部的，独立的循环中计算随机力和耗散力，该错误就会消失:

Nevertheless, if I compute the random and dissipative forces in an external, separate loop, the error disappears:

for i in range(npart):
    for d in range(dim):
        fd[i, d] = -gamma * v[i, d]
        fr[i, d] = noise/np.sqrt(dt) * np.random.normal()

两种计算之间有什么区别?在单独的循环中完成计算时，为什么没有错误?

What is the difference between both computations? Why there is no error when the computation is done in a separate loop?

推荐答案

已解决:如@micric所指出，第二个循环内有一个名为"fr"的变量，其类型为float.我犯了为数组使用相同名称的错误.因此，Python的抱怨.

SOLVED: As @micric pointed out, there is a variable inside the second loop called 'fr', which is of type float. I made the mistake of using the same name for an array. Hence Python's complaints.

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