LoadError在函数内调用@printf时发生

huangapple
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英文:

LoadError when calling @printf within a function

问题

ERROR: LoadError: UndefVarError: @printf not defined

英文:

I try to print a table of results within a function by calling the macro @printf. However, when I execute the code in Vscode (julia: execute the code in REPL), the interpreter throws a LoadError to me.
The code is following

  1. function mysqrt_step(a,x)
  2.     0.5*(a + a/x)
  3. end
  5. function mysqrt(a,x; tol = 1e-8)
  6.     iters = 0
  7.     x_prime = 0.0
  8.     Δ = 1000.0
  9.     
  10.     while dist > tol
  11.         x_prime = mysqrt_step(a,x)
  12.         Δ = abs(x - x_prime)
  13.         x = x_prime
  14.         iters += 1
  15.     end
  16.     
  17.     return(x,iters)
  18. end    
  20. using Printf  # use the Printf package (built-in)
  21. function sqrt_table()
  22.     @printf("%2s %10s %10s %10s \n", "a", "mysqrt", "sqrt", "Iterations")
  23.     for a in 2:10
  24.         tmp = mysqrt(a,a^2)
  25.         @printf("%2d %10f %10f %10d \n", a, tmp[1], sqrt(a), tmp[2])
  26.     end
  27. end

The error message is

> ERROR: LoadError: UndefVarError: @printf not defined

To be noticed, I have using Printf before defining the function

version information

  1. Julia Version 1.7.1
  2. Commit ac5cc99908 (2021-12-22 19:35 UTC)
  3. Platform Info:
  4.   OS: Windows (x86_64-w64-mingw32)
  5.   CPU: Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz
  6.   WORD_SIZE: 64
  7.   LIBM: libopenlibm
  8.   LLVM: libLLVM-12.0.1 (ORCJIT, skylake)
  9. Environment:
  10.   JULIA_EDITOR = code
  11.   JULIA_NUM_THREADS =

答案1

得分: 1

以下是翻译好的内容：

"Thanks for providing a minimum working example, but do make sure to re-run it in a fresh Julia session to make sure it actually reproduces your problem.

When I copy paste your code into a fresh Julia 1.7 session and run the sqrt_table() function, I get:

  1. julia> sqrt_table()
  2.  a     mysqrt       sqrt Iterations
  3. ERROR: UndefVarError: dist not defined
  4. Stacktrace:
  5.  [1] mysqrt(a::Int64, x::Int64; tol::Float64)
  6.    @ Main .\REPL[2]:6

So as Bill says in his comment, the error here is that the reference to dist in the while loop is undefined, and you probably meant to write while Δ > tol.

Also note that before the function errors, it prints the header line that you put into sqrt_table(), so there's actually no issue with Printf in your code.

With the distance variable name fixed, your code returns:

  1. julia> sqrt_table()
  2.  a     mysqrt       sqrt Iterations
  3.  2   1.618034   1.414214         21
  4.  3   2.186141   1.732051         18
  5.  4   2.732051   2.000000         16
  6.  5   3.265564   2.236068         15
  7.  6   3.791288   2.449490         14
  8.  7   4.311738   2.645751         14
  9.  8   4.828427   2.828427         13
  10.  9   5.342329   3.000000         12
  11. 10   5.854102   3.162278         12
英文:

Thanks for providing a minimum working example, but do make sure to re-run it in a fresh Julia session to make sure it actually reproduces your problem.

When I copy paste your code into a fresh Julia 1.7 session and run the sqrt_table() function, I get:

  1. julia> sqrt_table()
  2.  a     mysqrt       sqrt Iterations
  3. ERROR: UndefVarError: dist not defined
  4. Stacktrace:
  5.  [1] mysqrt(a::Int64, x::Int64; tol::Float64)
  6.    @ Main .\REPL[2]:6

So as Bill says in his comment, the error here is that the reference to dist in the while loop is undefined, and you probably meant to write while Δ > tol.

Also note that before the function errors, it prints the header line that you put into sqrt_table(), so there's actually no issue with Printf in your code.

With the distance variable name fixed, your code returns:

  1. julia> sqrt_table()
  2.  a     mysqrt       sqrt Iterations
  3.  2   1.618034   1.414214         21
  4.  3   2.186141   1.732051         18
  5.  4   2.732051   2.000000         16
  6.  5   3.265564   2.236068         15
  7.  6   3.791288   2.449490         14
  8.  7   4.311738   2.645751         14
  9.  8   4.828427   2.828427         13
  10.  9   5.342329   3.000000         12
  11. 10   5.854102   3.162278         12

huangapple
  • 本文由 发表于 2023年2月24日 10:13:24
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