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I would like to produce a table

Table1=Table[{j,j^2},{j,0.0001,Pi,Deltaj}]

where Deltaj is 0.0001 for j < 5*10^-3 and 0.01 otherwise. How to do this?

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Define the $j$-dependent step size:

Δ[j_] = Piecewise[{{0.0001, j < 5*10^-3}, {0.01, j >= 5*10^-3}}];

Make a list of $j$-values to use:

With[{start = 0.0001, end = π},
  jvalues = NestWhileList[# + Δ[#] &, start, # <= end &, 1, ∞, -1]]

{0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015, 0.0016, 0.0017, 0.0018, 0.0019, 0.002, 0.0021, 0.0022, 0.0023, 0.0024, 0.0025, 0.0026, 0.0027, 0.0028, 0.0029, 0.003, 0.0031, 0.0032, 0.0033, 0.0034, 0.0035, 0.0036, 0.0037, 0.0038, 0.0039, 0.004, 0.0041, 0.0042, 0.0043, 0.0044, 0.0045, 0.0046, 0.0047, 0.0048, 0.0049, 0.005, 0.015, 0.025, 0.035, 0.045, 0.055, 0.065, ..., 3.115, 3.125, 3.135}

Evaluate the table over these $j$-values:

Table[{j, j^2}, {j, jvalues}]

{{0.0001, 1.*10^-8}, {0.0002, 4.*10^-8}, {0.0003, 9.*10^-8}, {0.0004, 1.6*10^-7}, {0.0005, 2.5*10^-7}, {0.0006, 3.6*10^-7}, {0.0007, 4.9*10^-7}, {0.0008, 6.4*10^-7}, {0.0009, 8.1*10^-7}, {0.001, 1.*10^-6}, {0.0011, 1.21*10^-6}, {0.0012, 1.44*10^-6}, {0.0013, 1.69*10^-6}, {0.0014, 1.96*10^-6}, {0.0015, 2.25*10^-6}, {0.0016, 2.56*10^-6}, {0.0017, 2.89*10^-6}, {0.0018, 3.24*10^-6}, {0.0019, 3.61*10^-6}, {0.002, 4.*10^-6}, {0.0021, 4.41*10^-6}, {0.0022, 4.84*10^-6}, {0.0023, 5.29*10^-6}, {0.0024, 5.76*10^-6}, {0.0025, 6.25*10^-6}, {0.0026, 6.76*10^-6}, {0.0027, 7.29*10^-6}, {0.0028, 7.84*10^-6}, {0.0029, 8.41*10^-6}, {0.003, 9.*10^-6}, {0.0031, 9.61*10^-6}, {0.0032, 0.00001024}, {0.0033, 0.00001089}, {0.0034, 0.00001156}, {0.0035, 0.00001225}, {0.0036, 0.00001296}, {0.0037, 0.00001369}, {0.0038, 0.00001444}, {0.0039, 0.00001521}, {0.004, 0.000016}, {0.0041, 0.00001681}, {0.0042, 0.00001764}, {0.0043, 0.00001849}, {0.0044, 0.00001936}, {0.0045, 0.00002025}, {0.0046, 0.00002116}, {0.0047, 0.00002209}, {0.0048, 0.00002304}, {0.0049, 0.00002401}, {0.005, 0.000025}, {0.015, 0.000225}, {0.025, 0.000625}, {0.035, 0.001225}, {0.045, 0.002025}, {0.055, 0.003025}, {0.065, 0.004225}, ..., {3.115, 9.70322}, {3.125, 9.76562}, {3.135, 9.82822}}

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 Union[
 Table[{j, j^2}, {j, 0, .005, .0001}],
 Table[{j, j^2}, {j, 0.005, .05, .001}]
 ]

or

timelist = Table[Exp[j], {j, 1, 10}];
Table[{timelist[[i]], timelist[[i]]^2}, {i, Length[timelist]}
 ]
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  • $\begingroup$ Thank you. However, I am looking for something like Deltaj[j] which takes different values for different js. $\endgroup$ – John Taylor Jun 11 at 20:30

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