I'm writing a math equation inside which I have to express curly brackets. What I intend to write should look like {h_n}^infinity_0

My code is:

    The problem asks for estimates of the sizes of the coefficients $\{h_{n}\}\limit_{0}^{\infty}$.

While the preview shows this as exactly what I want, when I try compiling it I get an error message that calls it an "undefined control sequence".

I don't understand why: could anyone help explain this?

  • 2
    You are probably looking for \limits, not \limit.
    – Werner
    Feb 28 '15 at 19:22

I wouldn't use \limits in this case since it'll end up placing the lower and upper limits of the sequence below and above the right-hand curly brace -- probably not what you intended.

If you write \{h_{n}\}_{0}^{\infty}$ (see the middle example below, labelled "not awful"), the upper and lower limits may look like they're too close to each other, especially in text-style math mode. One way to fix this is to encase the closing curly brace, \}, in a pair of braces to change its status from "math-close" to "math-ordinary"; doing so will loosen the spacing quite a bit.

It may be best, though, to define a custom macro called, say, \seqwlimits to standardize the task at hand and to assure adequate vertical separation of the upper and lower limits.

enter image description here

huh??    & ${\{h_{n}\}}\limits_{0}^{\infty}$\\[2ex]
awful    & $\{h_{n}\}\limits_{0}^{\infty}$\\[2ex]
not awful& $\{h_{n}\}_{0}^{\infty}$\\[2ex]
better   & $\{h_{n}{\}}_{0}^{\infty}$\\[2ex]  % note the extra { and }
best     & $\seqwlimits{h_n}{0}{\infty}$\\
  • I agree that your best solution is better than your better solution, which is better than the bad one. So, why isn't \mathstrut used by default? Is it better only with 2 scripts?
    – Sigur
    Feb 28 '15 at 19:46
  • 1
    @sigur - I've modified my answer to provide two more possibilities. By default, \} (the closing curly brace) is assigned state "math-close" by TeX, and any subsequent sub- and superscripts are set in very tight mode by design. One way to overcome the cramped look is to change the state of the closing curly brace to "math-ordinary", e.g., by encasing it in curly braces (see the case labelled "better" in the example). To get even better spacing, IMNSHO, I suggest using \mathstrut directives, which insert invisible objects with height and depth of parentheses.
    – Mico
    Feb 28 '15 at 20:10
  • I ended up getting a similar error to my original one when I tried your Best solution, but your Not Awful and Better work great. Thank you very much!
    – Sammieo
    Mar 1 '15 at 15:35

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